Split out and export the number of configured user return MSRs so that
VMX can iterate over the set of MSRs without having to do its own tracking.
Keep the list itself internal to x86 so that vendor code still has to go
through the "official" APIs to add/modify entries.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-13-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Tag TSX_CTRL as not needing to be loaded when RTM isn't supported in the
host. Crushing the write mask to '0' has the same effect, but requires
more mental gymnastics to understand.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-12-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Drop VMX's global list of user return MSRs now that VMX doesn't resort said
list to isolate "active" MSRs, i.e. now that VMX's list and x86's list have
the same MSRs in the same order.
In addition to eliminating the redundant list, this will also allow moving
more of the list management into common x86.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-11-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Explicitly flag a uret MSR as needing to be loaded into hardware instead of
resorting the list of "active" MSRs and tracking how many MSRs in total
need to be loaded. The only benefit to sorting the list is that the loop
to load MSRs during vmx_prepare_switch_to_guest() doesn't need to iterate
over all supported uret MRS, only those that are active. But that is a
pointless optimization, as the most common case, running a 64-bit guest,
will load the vast majority of MSRs. Not to mention that a single WRMSR is
far more expensive than iterating over the list.
Providing a stable list order obviates the need to track a given MSR's
"slot" in the per-CPU list of user return MSRs; all lists simply use the
same ordering. Future patches will take advantage of the stable order to
further simplify the related code.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-10-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Configure the list of user return MSRs that are actually supported at
module init instead of reprobing the list of possible MSRs every time a
vCPU is created. Curating the list on a per-vCPU basis is pointless; KVM
is completely hosed if the set of supported MSRs changes after module init,
or if the set of MSRs differs per physical PCU.
The per-vCPU lists also increase complexity (see __vmx_find_uret_msr()) and
creates corner cases that _should_ be impossible, but theoretically exist
in KVM, e.g. advertising RDTSCP to userspace without actually being able to
virtualize RDTSCP if probing MSR_TSC_AUX fails.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-9-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Allow userspace to enable RDPID for a guest without also enabling RDTSCP.
Aside from checking for RDPID support in the obvious flows, VMX also needs
to set ENABLE_RDTSCP=1 when RDPID is exposed.
For the record, there is no known scenario where enabling RDPID without
RDTSCP is desirable. But, both AMD and Intel architectures allow for the
condition, i.e. this is purely to make KVM more architecturally accurate.
Fixes: 41cd02c6f7 ("kvm: x86: Expose RDPID in KVM_GET_SUPPORTED_CPUID")
Cc: stable@vger.kernel.org
Reported-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-8-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Probe MSR_TSC_AUX whether or not RDTSCP is supported in the host, and
if probing succeeds, load the guest's MSR_TSC_AUX into hardware prior to
VMRUN. Because SVM doesn't support interception of RDPID, RDPID cannot
be disallowed in the guest (without resorting to binary translation).
Leaving the host's MSR_TSC_AUX in hardware would leak the host's value to
the guest if RDTSCP is not supported.
Note, there is also a kernel bug that prevents leaking the host's value.
The host kernel initializes MSR_TSC_AUX if and only if RDTSCP is
supported, even though the vDSO usage consumes MSR_TSC_AUX via RDPID.
I.e. if RDTSCP is not supported, there is no host value to leak. But,
if/when the host kernel bug is fixed, KVM would start leaking MSR_TSC_AUX
in the case where hardware supports RDPID but RDTSCP is unavailable for
whatever reason.
Probing MSR_TSC_AUX will also allow consolidating the probe and define
logic in common x86, and will make it simpler to condition the existence
of MSR_TSX_AUX (from the guest's perspective) on RDTSCP *or* RDPID.
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-7-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Disable preemption when probing a user return MSR via RDSMR/WRMSR. If
the MSR holds a different value per logical CPU, the WRMSR could corrupt
the host's value if KVM is preempted between the RDMSR and WRMSR, and
then rescheduled on a different CPU.
Opportunistically land the helper in common x86, SVM will use the helper
in a future commit.
Fixes: 4be5341026 ("KVM: VMX: Initialize vmx->guest_msrs[] right after allocation")
Cc: stable@vger.kernel.org
Cc: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-6-seanjc@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Add a dedicated intercept enum for RDPID instead of piggybacking RDTSCP.
Unlike VMX's ENABLE_RDTSCP, RDPID is not bound to SVM's RDTSCP intercept.
Fixes: fb6d4d340e ("KVM: x86: emulate RDPID")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-5-seanjc@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Intercept RDTSCP to inject #UD if RDTSC is disabled in the guest.
Note, SVM does not support intercepting RDPID. Unlike VMX's
ENABLE_RDTSCP control, RDTSCP interception does not apply to RDPID. This
is a benign virtualization hole as the host kernel (incorrectly) sets
MSR_TSC_AUX if RDTSCP is supported, and KVM loads the guest's MSR_TSC_AUX
into hardware if RDTSCP is supported in the host, i.e. KVM will not leak
the host's MSR_TSC_AUX to the guest.
But, when the kernel bug is fixed, KVM will start leaking the host's
MSR_TSC_AUX if RDPID is supported in hardware, but RDTSCP isn't available
for whatever reason. This leak will be remedied in a future commit.
Fixes: 46896c73c1 ("KVM: svm: add support for RDTSCP")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-4-seanjc@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Do not advertise emulation support for RDPID if RDTSCP is unsupported.
RDPID emulation subtly relies on MSR_TSC_AUX to exist in hardware, as
both vmx_get_msr() and svm_get_msr() will return an error if the MSR is
unsupported, i.e. ctxt->ops->get_msr() will fail and the emulator will
inject a #UD.
Note, RDPID emulation also relies on RDTSCP being enabled in the guest,
but this is a KVM bug and will eventually be fixed.
Fixes: fb6d4d340e ("KVM: x86: emulate RDPID")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-3-seanjc@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Clear KVM's RDPID capability if the ENABLE_RDTSCP secondary exec control is
unsupported. Despite being enumerated in a separate CPUID flag, RDPID is
bundled under the same VMCS control as RDTSCP and will #UD in VMX non-root
if ENABLE_RDTSCP is not enabled.
Fixes: 41cd02c6f7 ("kvm: x86: Expose RDPID in KVM_GET_SUPPORTED_CPUID")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-2-seanjc@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
While in most cases, when returning to use the VMCB01,
the exit reason stored in it will be SVM_EXIT_VMRUN,
on first VM exit after a nested migration this field
can contain anything since the VM entry did happen
before the migration.
Remove this warning to avoid the false positive.
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210504143936.1644378-3-mlevitsk@redhat.com>
Fixes: 9a7de6ecc3 ("KVM: nSVM: If VMRUN is single-stepped, queue the #DB intercept in nested_svm_vmexit()")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
While usually the L1's GIF is set while L2 runs, and usually
migration nested state is loaded after a vCPU reset which
also sets L1's GIF to true, this is not guaranteed.
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210504143936.1644378-2-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
In ioctl KVM_X86_SET_MSR_FILTER, input from user space is validated
after a memdup_user(). For invalid inputs we'd memdup and then call
kfree unnecessarily. Hoist input validation to avoid kfree altogether.
Signed-off-by: Siddharth Chandrasekaran <sidcha@amazon.de>
Message-Id: <20210503122111.13775-1-sidcha@amazon.de>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Clang's integrated assembler does not allow symbols with non-absolute
values to be reassigned. Modify the interrupt entry loop macro to be
compatible with IAS by using a label and an offset.
Cc: Jian Cai <caij2003@gmail.com>
Signed-off-by: Bill Wendling <morbo@google.com>
References: https://lore.kernel.org/lkml/20200714233024.1789985-1-caij2003@gmail.com/
Message-Id: <20201211012317.3722214-1-morbo@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Add a test for the regression, introduced by commit f2c7ef3ba9
("KVM: nSVM: cancel KVM_REQ_GET_NESTED_STATE_PAGES on nested vmexit"). When
L2->L1 exit is forced immediately after restoring nested state,
KVM_REQ_GET_NESTED_STATE_PAGES request is cleared and VMCS12 changes
(e.g. fresh RIP) are not reflected to eVMCS. The consequent nested
vCPU run gets broken.
Utilize NMI injection to do the job.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210505151823.1341678-3-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
'run->exit_reason == KVM_EXIT_SHUTDOWN' check is not ideal as we may be
getting some unexpected exception. Directly check for #UD instead.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210505151823.1341678-2-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
When enlightened VMCS is in use and nested state is migrated with
vmx_get_nested_state()/vmx_set_nested_state() KVM can't map evmcs
page right away: evmcs gpa is not 'struct kvm_vmx_nested_state_hdr'
and we can't read it from VP assist page because userspace may decide
to restore HV_X64_MSR_VP_ASSIST_PAGE after restoring nested state
(and QEMU, for example, does exactly that). To make sure eVMCS is
mapped /vmx_set_nested_state() raises KVM_REQ_GET_NESTED_STATE_PAGES
request.
Commit f2c7ef3ba9 ("KVM: nSVM: cancel KVM_REQ_GET_NESTED_STATE_PAGES
on nested vmexit") added KVM_REQ_GET_NESTED_STATE_PAGES clearing to
nested_vmx_vmexit() to make sure MSR permission bitmap is not switched
when an immediate exit from L2 to L1 happens right after migration (caused
by a pending event, for example). Unfortunately, in the exact same
situation we still need to have eVMCS mapped so
nested_sync_vmcs12_to_shadow() reflects changes in VMCS12 to eVMCS.
As a band-aid, restore nested_get_evmcs_page() when clearing
KVM_REQ_GET_NESTED_STATE_PAGES in nested_vmx_vmexit(). The 'fix' is far
from being ideal as we can't easily propagate possible failures and even if
we could, this is most likely already too late to do so. The whole
'KVM_REQ_GET_NESTED_STATE_PAGES' idea for mapping eVMCS after migration
seems to be fragile as we diverge too much from the 'native' path when
vmptr loading happens on vmx_set_nested_state().
Fixes: f2c7ef3ba9 ("KVM: nSVM: cancel KVM_REQ_GET_NESTED_STATE_PAGES on nested vmexit")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210503150854.1144255-2-vkuznets@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The capability that exposes new ioctl KVM_X86_SET_MSR_FILTER to
userspace is specified incorrectly as the ioctl itself (instead of
KVM_CAP_X86_MSR_FILTER). This patch fixes it.
Fixes: 1a155254ff ("KVM: x86: Introduce MSR filtering")
Reviewed-by: Alexander Graf <graf@amazon.de>
Signed-off-by: Siddharth Chandrasekaran <sidcha@amazon.de>
Message-Id: <20210503120059.9283-1-sidcha@amazon.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Simplify the code by making PV features shutdown happen in one place.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210414123544.1060604-6-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Crash shutdown handler only disables kvmclock and steal time, other PV
features remain active so we risk corrupting memory or getting some
side-effects in kdump kernel. Move crash handler to kvm.c and unify
with CPU offline.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210414123544.1060604-5-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Currenly, we disable kvmclock from machine_shutdown() hook and this
only happens for boot CPU. We need to disable it for all CPUs to
guard against memory corruption e.g. on restore from hibernate.
Note, writing '0' to kvmclock MSR doesn't clear memory location, it
just prevents hypervisor from updating the location so for the short
while after write and while CPU is still alive, the clock remains usable
and correct so we don't need to switch to some other clocksource.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210414123544.1060604-4-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Various PV features (Async PF, PV EOI, steal time) work through memory
shared with hypervisor and when we restore from hibernation we must
properly teardown all these features to make sure hypervisor doesn't
write to stale locations after we jump to the previously hibernated kernel
(which can try to place anything there). For secondary CPUs the job is
already done by kvm_cpu_down_prepare(), register syscore ops to do
the same for boot CPU.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210414123544.1060604-3-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
User space could ask for very large hash tables, we need to make sure
our size computations wont overflow.
nf_tables_newset() needs to double check the u64 size
will fit into size_t field.
Fixes: 0ed6389c48 ("netfilter: nf_tables: rename set implementations")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
succed -> succeed in mm/hugetlb.c
wil -> will in mm/mempolicy.c
wit -> with in mm/page_alloc.c
Retruns -> Returns in mm/page_vma_mapped.c
confict -> conflict in mm/secretmem.c
No functionality changed.
Link: https://lkml.kernel.org/r/20210408140027.60623-1-lujialin4@huawei.com
Signed-off-by: Lu Jialin <lujialin4@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The section "19) Editor modelines and other cruft" in
Documentation/process/coding-style.rst clearly says, "Do not include any
of these in source files."
I recently receive a patch to explicitly add a new one.
Let's do treewide cleanups, otherwise some people follow the existing code
and attempt to upstream their favoriate editor setups.
It is even nicer if scripts/checkpatch.pl can check it.
If we like to impose coding style in an editor-independent manner, I think
editorconfig (patch [1]) is a saner solution.
[1] https://lore.kernel.org/lkml/20200703073143.423557-1-danny@kdrag0n.dev/
Link: https://lkml.kernel.org/r/20210324054457.1477489-1-masahiroy@kernel.org
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org> [auxdisplay]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
change 'infite' to 'infinite'
change 'concurent' to 'concurrent'
change 'memvers' to 'members'
change 'decendants' to 'descendants'
change 'argumets' to 'arguments'
Link: https://lkml.kernel.org/r/20210316112904.10661-1-cxfcosmos@gmail.com
Signed-off-by: Xiaofeng Cao <caoxiaofeng@yulong.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Fix some spelling mistakes, and modify the order of the parameter comments
to be consistent with the order of the parameters passed to the function.
Link: https://lkml.kernel.org/r/1615636139-4076-1-git-send-email-zhouchuangao@vivo.com
Signed-off-by: zhouchuangao <zhouchuangao@vivo.com>
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Few spelling fixes throughout the file.
Link: https://lkml.kernel.org/r/20210318201404.6380-1-unixbhaskar@gmail.com
Signed-off-by: Bhaskar Chowdhury <unixbhaskar@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
There is a spelling mistake in a comment. Fix it.
Link: https://lkml.kernel.org/r/20210317094158.5762-1-colin.king@canonical.com
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
In case of a use after free kernel oops, the freeing path of the object
is required to debug futher. In most of cases the object address is
present in one of the registers.
Thus check the register's address and if it belongs to slab, print its
alloc and free path.
e.g. in the below issue register r6 belongs to slab, and a use after
free issue occurred on one of its dereferenced values:
Unable to handle kernel paging request at virtual address 6b6b6b6f
....
pc : [<c0538afc>] lr : [<c0465674>] psr: 60000013
sp : c8927d40 ip : ffffefff fp : c8aa8020
r10: c8927e10 r9 : 00000001 r8 : 00400cc0
r7 : 00000000 r6 : c8ab0180 r5 : c1804a80 r4 : c8aa8008
r3 : c1a5661c r2 : 00000000 r1 : 6b6b6b6b r0 : c139bf48
.....
Register r6 information: slab kmalloc-64 start c8ab0140 data offset 64 pointer offset 0 size 64 allocated at meminfo_proc_show+0x40/0x4fc
meminfo_proc_show+0x40/0x4fc
seq_read_iter+0x18c/0x4c4
proc_reg_read_iter+0x84/0xac
generic_file_splice_read+0xe8/0x17c
splice_direct_to_actor+0xb8/0x290
do_splice_direct+0xa0/0xe0
do_sendfile+0x2d0/0x438
sys_sendfile64+0x12c/0x140
ret_fast_syscall+0x0/0x58
0xbeeacde4
Free path:
meminfo_proc_show+0x5c/0x4fc
seq_read_iter+0x18c/0x4c4
proc_reg_read_iter+0x84/0xac
generic_file_splice_read+0xe8/0x17c
splice_direct_to_actor+0xb8/0x290
do_splice_direct+0xa0/0xe0
do_sendfile+0x2d0/0x438
sys_sendfile64+0x12c/0x140
ret_fast_syscall+0x0/0x58
0xbeeacde4
Link: https://lkml.kernel.org/r/1615891032-29160-3-git-send-email-maninder1.s@samsung.com
Co-developed-by: Vaneet Narang <v.narang@samsung.com>
Signed-off-by: Vaneet Narang <v.narang@samsung.com>
Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The last user (/dev/kmem) is gone. Let's drop it.
Link: https://lkml.kernel.org/r/20210324102351.6932-4-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: huang ying <huang.ying.caritas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Patch series "drivers/char: remove /dev/kmem for good".
Exploring /dev/kmem and /dev/mem in the context of memory hot(un)plug and
memory ballooning, I started questioning the existence of /dev/kmem.
Comparing it with the /proc/kcore implementation, it does not seem to be
able to deal with things like
a) Pages unmapped from the direct mapping (e.g., to be used by secretmem)
-> kern_addr_valid(). virt_addr_valid() is not sufficient.
b) Special cases like gart aperture memory that is not to be touched
-> mem_pfn_is_ram()
Unless I am missing something, it's at least broken in some cases and might
fault/crash the machine.
Looks like its existence has been questioned before in 2005 and 2010 [1],
after ~11 additional years, it might make sense to revive the discussion.
CONFIG_DEVKMEM is only enabled in a single defconfig (on purpose or by
mistake?). All distributions disable it: in Ubuntu it has been disabled
for more than 10 years, in Debian since 2.6.31, in Fedora at least
starting with FC3, in RHEL starting with RHEL4, in SUSE starting from
15sp2, and OpenSUSE has it disabled as well.
1) /dev/kmem was popular for rootkits [2] before it got disabled
basically everywhere. Ubuntu documents [3] "There is no modern user of
/dev/kmem any more beyond attackers using it to load kernel rootkits.".
RHEL documents in a BZ [5] "it served no practical purpose other than to
serve as a potential security problem or to enable binary module drivers
to access structures/functions they shouldn't be touching"
2) /proc/kcore is a decent interface to have a controlled way to read
kernel memory for debugging puposes. (will need some extensions to
deal with memory offlining/unplug, memory ballooning, and poisoned
pages, though)
3) It might be useful for corner case debugging [1]. KDB/KGDB might be a
better fit, especially, to write random memory; harder to shoot
yourself into the foot.
4) "Kernel Memory Editor" [4] hasn't seen any updates since 2000 and seems
to be incompatible with 64bit [1]. For educational purposes,
/proc/kcore might be used to monitor value updates -- or older
kernels can be used.
5) It's broken on arm64, and therefore, completely disabled there.
Looks like it's essentially unused and has been replaced by better
suited interfaces for individual tasks (/proc/kcore, KDB/KGDB). Let's
just remove it.
[1] https://lwn.net/Articles/147901/
[2] https://www.linuxjournal.com/article/10505
[3] https://wiki.ubuntu.com/Security/Features#A.2Fdev.2Fkmem_disabled
[4] https://sourceforge.net/projects/kme/
[5] https://bugzilla.redhat.com/show_bug.cgi?id=154796
Link: https://lkml.kernel.org/r/20210324102351.6932-1-david@redhat.com
Link: https://lkml.kernel.org/r/20210324102351.6932-2-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Alexander A. Klimov" <grandmaster@al2klimov.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Andrey Zhizhikin <andrey.zhizhikin@leica-geosystems.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Brian Cain <bcain@codeaurora.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Chris Zankel <chris@zankel.net>
Cc: Corentin Labbe <clabbe@baylibre.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Greentime Hu <green.hu@gmail.com>
Cc: Gregory Clement <gregory.clement@bootlin.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Hillf Danton <hdanton@sina.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: James Troup <james.troup@canonical.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kairui Song <kasong@redhat.com>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Niklas Schnelle <schnelle@linux.ibm.com>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Cc: openrisc@lists.librecores.org
Cc: Palmer Dabbelt <palmerdabbelt@google.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: "Pavel Machek (CIP)" <pavel@denx.de>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Pierre Morel <pmorel@linux.ibm.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Rich Felker <dalias@libc.org>
Cc: Robert Richter <rric@kernel.org>
Cc: Rob Herring <robh@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Cc: sparclinux@vger.kernel.org
Cc: Stafford Horne <shorne@gmail.com>
Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Theodore Dubois <tblodt@icloud.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: William Cohen <wcohen@redhat.com>
Cc: Xiaoming Ni <nixiaoming@huawei.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Allow the developer to specifiy the initial value of the modprobe_path[]
string. This can be used to set it to the empty string initially, thus
effectively disabling request_module() during early boot until userspace
writes a new value via the /proc/sys/kernel/modprobe interface. [1]
When building a custom kernel (often for an embedded target), it's normal
to build everything into the kernel that is needed for booting, and indeed
the initramfs often contains no modules at all, so every such
request_module() done before userspace init has mounted the real rootfs is
a waste of time.
This is particularly useful when combined with the previous patch, which
made the initramfs unpacking asynchronous - for that to work, it had to
make any usermodehelper call wait for the unpacking to finish before
attempting to invoke the userspace helper. By eliminating all such
(known-to-be-futile) calls of usermodehelper, the initramfs unpacking and
the {device,late}_initcalls can proceed in parallel for much longer.
For a relatively slow ppc board I'm working on, the two patches combined
lead to 0.2s faster boot - but more importantly, the fact that the
initramfs unpacking proceeds completely in the background while devices
get probed means I get to handle the gpio watchdog in time without getting
reset.
[1] __request_module() already has an early -ENOENT return when
modprobe_path is the empty string.
Link: https://lkml.kernel.org/r/20210313212528.2956377-3-linux@rasmusvillemoes.dk
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Jessica Yu <jeyu@kernel.org>
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Patch series "background initramfs unpacking, and CONFIG_MODPROBE_PATH", v3.
These two patches are independent, but better-together.
The second is a rather trivial patch that simply allows the developer to
change "/sbin/modprobe" to something else - e.g. the empty string, so
that all request_module() during early boot return -ENOENT early, without
even spawning a usermode helper, needlessly synchronizing with the
initramfs unpacking.
The first patch delegates decompressing the initramfs to a worker thread,
allowing do_initcalls() in main.c to proceed to the device_ and late_
initcalls without waiting for that decompression (and populating of
rootfs) to finish. Obviously, some of those later calls may rely on the
initramfs being available, so I've added synchronization points in the
firmware loader and usermodehelper paths - there might be other places
that would need this, but so far no one has been able to think of any
places I have missed.
There's not much to win if most of the functionality needed during boot is
only available as modules. But systems with a custom-made .config and
initramfs can boot faster, partly due to utilizing more than one cpu
earlier, partly by avoiding known-futile modprobe calls (which would still
trigger synchronization with the initramfs unpacking, thus eliminating
most of the first benefit).
This patch (of 2):
Most of the boot process doesn't actually need anything from the
initramfs, until of course PID1 is to be executed. So instead of doing
the decompressing and populating of the initramfs synchronously in
populate_rootfs() itself, push that off to a worker thread.
This is primarily motivated by an embedded ppc target, where unpacking
even the rather modest sized initramfs takes 0.6 seconds, which is long
enough that the external watchdog becomes unhappy that it doesn't get
attention soon enough. By doing the initramfs decompression in a worker
thread, we get to do the device_initcalls and hence start petting the
watchdog much sooner.
Normal desktops might benefit as well. On my mostly stock Ubuntu kernel,
my initramfs is a 26M xz-compressed blob, decompressing to around 126M.
That takes almost two seconds:
[ 0.201454] Trying to unpack rootfs image as initramfs...
[ 1.976633] Freeing initrd memory: 29416K
Before this patch, these lines occur consecutively in dmesg. With this
patch, the timestamps on these two lines is roughly the same as above, but
with 172 lines inbetween - so more than one cpu has been kept busy doing
work that would otherwise only happen after the populate_rootfs()
finished.
Should one of the initcalls done after rootfs_initcall time (i.e., device_
and late_ initcalls) need something from the initramfs (say, a kernel
module or a firmware blob), it will simply wait for the initramfs
unpacking to be done before proceeding, which should in theory make this
completely safe.
But if some driver pokes around in the filesystem directly and not via one
of the official kernel interfaces (i.e. request_firmware*(),
call_usermodehelper*) that theory may not hold - also, I certainly might
have missed a spot when sprinkling wait_for_initramfs(). So there is an
escape hatch in the form of an initramfs_async= command line parameter.
Link: https://lkml.kernel.org/r/20210313212528.2956377-1-linux@rasmusvillemoes.dk
Link: https://lkml.kernel.org/r/20210313212528.2956377-2-linux@rasmusvillemoes.dk
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Sean Christopherson