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signal/x86: Call force_sig_pkuerr from __bad_area_nosemaphore 

There is only one code path that can generate a pkuerr signal.  That
code path calls __bad_area_nosemaphore and can be dectected by testing
if si_code == SEGV_PKUERR.  It can be seen from inspection that all of
the other tests in fill_sig_info_pkey are unnecessary.

Therefore call force_sig_pkuerr directly from __bad_area_semaphore and
remove fill_sig_info_pkey.

At the same time move the comment above force_sig_info_pkey into
bad_area_access_error, so that the documentation about pkey generation
races is not lost.

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2018-09-18 01:23:35 +02:00
parent aba1ecd32c
commit 9db812dbb2
1 changed files with 24 additions and 52 deletions
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76
arch/x86/mm/fault.c
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@ -153,56 +153,6 @@ is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
return prefetch;
}
/*
* A protection key fault means that the PKRU value did not allow
* access to some PTE. Userspace can figure out what PKRU was
* from the XSAVE state, and this function fills out a field in
* siginfo so userspace can discover which protection key was set
* on the PTE.
*
* If we get here, we know that the hardware signaled a X86_PF_PK
* fault and that there was a VMA once we got in the fault
* handler. It does *not* guarantee that the VMA we find here
* was the one that we faulted on.
*
* 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4);
* 2. T1 : set PKRU to deny access to pkey=4, touches page
* 3. T1 : faults...
* 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5);
* 5. T1 : enters fault handler, takes mmap_sem, etc...
* 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really
* faulted on a pte with its pkey=4.
*/
static void fill_sig_info_pkey(int si_signo, int si_code, siginfo_t *info,
u32 *pkey)
{
/* This is effectively an #ifdef */
if (!boot_cpu_has(X86_FEATURE_OSPKE))
return;
/* Fault not from Protection Keys: nothing to do */
if ((si_code != SEGV_PKUERR) || (si_signo != SIGSEGV))
return;
/*
* force_sig_info_fault() is called from a number of
* contexts, some of which have a VMA and some of which
* do not. The X86_PF_PK handing happens after we have a
* valid VMA, so we should never reach this without a
* valid VMA.
*/
if (!pkey) {
WARN_ONCE(1, "PKU fault with no VMA passed in");
info->si_pkey = 0;
return;
}
/*
* si_pkey should be thought of as a strong hint, but not
* absolutely guranteed to be 100% accurate because of
* the race explained above.
*/
info->si_pkey = *pkey;
}
static void
force_sig_info_fault(int si_signo, int si_code, unsigned long address,
struct task_struct *tsk, u32 *pkey)
@ -215,8 +165,6 @@ force_sig_info_fault(int si_signo, int si_code, unsigned long address,
info.si_code = si_code;
info.si_addr = (void __user *)address;
fill_sig_info_pkey(si_signo, si_code, &info, pkey);
force_sig_info(si_signo, &info, tsk);
}
@ -884,6 +832,9 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
tsk->thread.error_code = error_code;
tsk->thread.trap_nr = X86_TRAP_PF;
if (si_code == SEGV_PKUERR)
force_sig_pkuerr((void __user *)address, *pkey);
force_sig_info_fault(SIGSEGV, si_code, address, tsk, pkey);
return;
@ -949,7 +900,28 @@ bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
* if pkeys are compiled out.
*/
if (bad_area_access_from_pkeys(error_code, vma)) {
/*
* A protection key fault means that the PKRU value did not allow
* access to some PTE. Userspace can figure out what PKRU was
* from the XSAVE state. This function captures the pkey from
* the vma and passes it to userspace so userspace can discover
* which protection key was set on the PTE.
*
* If we get here, we know that the hardware signaled a X86_PF_PK
* fault and that there was a VMA once we got in the fault
* handler. It does *not* guarantee that the VMA we find here
* was the one that we faulted on.
*
* 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4);
* 2. T1 : set PKRU to deny access to pkey=4, touches page
* 3. T1 : faults...
* 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5);
* 5. T1 : enters fault handler, takes mmap_sem, etc...
* 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really
* faulted on a pte with its pkey=4.
*/
u32 pkey = vma_pkey(vma);
__bad_area(regs, error_code, address, &pkey, SEGV_PKUERR);
} else {
__bad_area(regs, error_code, address, NULL, SEGV_ACCERR);