Commit 4d516f41 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar

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: default avatarJosh 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.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 7252c4c3
...@@ -45,6 +45,7 @@ ...@@ -45,6 +45,7 @@
#include <asm/asm.h> #include <asm/asm.h>
#include <asm/smap.h> #include <asm/smap.h>
#include <asm/export.h> #include <asm/export.h>
#include <asm/frame.h>
.section .entry.text, "ax" .section .entry.text, "ax"
...@@ -237,6 +238,23 @@ ENTRY(__switch_to_asm) ...@@ -237,6 +238,23 @@ ENTRY(__switch_to_asm)
jmp __switch_to jmp __switch_to
END(__switch_to_asm) 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. * A newly forked process directly context switches into this address.
* *
...@@ -245,9 +263,7 @@ END(__switch_to_asm) ...@@ -245,9 +263,7 @@ END(__switch_to_asm)
* edi: kernel thread arg * edi: kernel thread arg
*/ */
ENTRY(ret_from_fork) ENTRY(ret_from_fork)
pushl %eax call schedule_tail_wrapper
call schedule_tail
popl %eax
testl %ebx, %ebx testl %ebx, %ebx
jnz 1f /* kernel threads are uncommon */ jnz 1f /* kernel threads are uncommon */
......
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