Commit 4d516f41 authored Sep 21, 2016 by Josh Poimboeuf Committed by Ingo Molnar Oct 20, 2016

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>

parent 7252c4c3

arch/x86/entry/entry_32.S

+19 −3

Original line number	Diff line number	Diff line
		@@ -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 */

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