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x86/entry/64: Move SWAPGS into the common IRET-to-usermode path 

All of the code paths that ended up doing IRET to usermode did
SWAPGS immediately beforehand.  Move the SWAPGS into the common
code.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/27fd6f45b7cd640de38fb9066fd0349bcd11f8e1.1509609304.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2017-11-02 00:59:00 -07:00 committed by Ingo Molnar
parent 26c4ef9c49
commit 8a055d7f41
2 changed files with 15 additions and 20 deletions
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32
arch/x86/entry/entry_64.S
View File

@ -249,12 +249,14 @@ return_from_SYSCALL_64:
/*
* Try to use SYSRET instead of IRET if we're returning to
* a completely clean 64-bit userspace context.
* a completely clean 64-bit userspace context. If we're not,
* go to the slow exit path.
*/
movq RCX(%rsp), %rcx
movq RIP(%rsp), %r11
cmpq %rcx, %r11 /* RCX == RIP */
jne opportunistic_sysret_failed
cmpq %rcx, %r11 /* SYSRET requires RCX == RIP */
jne swapgs_restore_regs_and_return_to_usermode
/*
* On Intel CPUs, SYSRET with non-canonical RCX/RIP will #GP
@ -272,14 +274,14 @@ return_from_SYSCALL_64:
/* If this changed %rcx, it was not canonical */
cmpq %rcx, %r11
jne opportunistic_sysret_failed
jne swapgs_restore_regs_and_return_to_usermode
cmpq $__USER_CS, CS(%rsp) /* CS must match SYSRET */
jne opportunistic_sysret_failed
jne swapgs_restore_regs_and_return_to_usermode
movq R11(%rsp), %r11
cmpq %r11, EFLAGS(%rsp) /* R11 == RFLAGS */
jne opportunistic_sysret_failed
jne swapgs_restore_regs_and_return_to_usermode
/*
* SYSCALL clears RF when it saves RFLAGS in R11 and SYSRET cannot
@ -300,12 +302,12 @@ return_from_SYSCALL_64:
* would never get past 'stuck_here'.
*/
testq $(X86_EFLAGS_RF|X86_EFLAGS_TF), %r11
jnz opportunistic_sysret_failed
jnz swapgs_restore_regs_and_return_to_usermode
/* nothing to check for RSP */
cmpq $__USER_DS, SS(%rsp) /* SS must match SYSRET */
jne opportunistic_sysret_failed
jne swapgs_restore_regs_and_return_to_usermode
/*
* We win! This label is here just for ease of understanding
@ -318,10 +320,6 @@ syscall_return_via_sysret:
movq RSP(%rsp), %rsp
UNWIND_HINT_EMPTY
USERGS_SYSRET64
opportunistic_sysret_failed:
SWAPGS
jmp restore_regs_and_return_to_usermode
END(entry_SYSCALL_64)
ENTRY(stub_ptregs_64)
@ -422,8 +420,7 @@ ENTRY(ret_from_fork)
movq %rsp, %rdi
call syscall_return_slowpath /* returns with IRQs disabled */
TRACE_IRQS_ON /* user mode is traced as IRQS on */
SWAPGS
jmp restore_regs_and_return_to_usermode
jmp swapgs_restore_regs_and_return_to_usermode
1:
/* kernel thread */
@ -611,9 +608,8 @@ GLOBAL(retint_user)
mov %rsp,%rdi
call prepare_exit_to_usermode
TRACE_IRQS_IRETQ
SWAPGS
GLOBAL(restore_regs_and_return_to_usermode)
GLOBAL(swapgs_restore_regs_and_return_to_usermode)
#ifdef CONFIG_DEBUG_ENTRY
/* Assert that pt_regs indicates user mode. */
testl $3, CS(%rsp)
@ -621,6 +617,7 @@ GLOBAL(restore_regs_and_return_to_usermode)
ud2
1:
#endif
SWAPGS
RESTORE_EXTRA_REGS
RESTORE_C_REGS
REMOVE_PT_GPREGS_FROM_STACK 8
@ -1342,8 +1339,7 @@ ENTRY(nmi)
* Return back to user mode. We must *not* do the normal exit
* work, because we don't want to enable interrupts.
*/
SWAPGS
jmp restore_regs_and_return_to_usermode
jmp swapgs_restore_regs_and_return_to_usermode
.Lnmi_from_kernel:
/*

3
arch/x86/entry/entry_64_compat.S
View File

@ -336,8 +336,7 @@ ENTRY(entry_INT80_compat)
/* Go back to user mode. */
TRACE_IRQS_ON
SWAPGS
jmp restore_regs_and_return_to_usermode
jmp swapgs_restore_regs_and_return_to_usermode
END(entry_INT80_compat)
ENTRY(stub32_clone)