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x86/entry/32: Fix the end of the stack for newly forked tasks 

Thanks to all the recent x86 entry code refactoring, most tasks' kernel
stacks start at the same offset right below their saved pt_regs,
regardless of which syscall was used to enter the kernel.  That creates
a nice convention which makes it straightforward to identify the end of
the stack, which can be useful for the unwinder to verify the stack is
sane.

Calling schedule_tail() directly breaks that convention because its an
asmlinkage function so its argument has to be pushed on the stack.  Add
a wrapper which creates a proper "end of stack" frame header before the
call.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nilay Vaish <nilayvaish@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/ecafcd882676bf48ceaf50483782552bb98476e5.1474480779.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Josh Poimboeuf 2016-09-21 16:04:01 -05:00 committed by Ingo Molnar
parent 7252c4c35e
commit 4d516f4170
1 changed files with 19 additions and 3 deletions
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22
arch/x86/entry/entry_32.S
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@ -45,6 +45,7 @@
#include <asm/asm.h>
#include <asm/smap.h>
#include <asm/export.h>
#include <asm/frame.h>
.section .entry.text, "ax"
@ -237,6 +238,23 @@ ENTRY(__switch_to_asm)
jmp __switch_to
END(__switch_to_asm)
/*
* The unwinder expects the last frame on the stack to always be at the same
* offset from the end of the page, which allows it to validate the stack.
* Calling schedule_tail() directly would break that convention because its an
* asmlinkage function so its argument has to be pushed on the stack. This
* wrapper creates a proper "end of stack" frame header before the call.
*/
ENTRY(schedule_tail_wrapper)
FRAME_BEGIN
pushl %eax
call schedule_tail
popl %eax
FRAME_END
ret
ENDPROC(schedule_tail_wrapper)
/*
* A newly forked process directly context switches into this address.
*
@ -245,9 +263,7 @@ END(__switch_to_asm)
* edi: kernel thread arg
*/
ENTRY(ret_from_fork)
pushl %eax
call schedule_tail
popl %eax
call schedule_tail_wrapper
testl %ebx, %ebx
jnz 1f /* kernel threads are uncommon */