x86/entry: Fix the end of the stack for newly forked tasks (ff3f7e24) · Commits · 戴 / test

When unwinding a task, the end of the stack is always at the same offset right below the saved pt_regs, regardless of which syscall was used to enter the kernel. That convention allows the unwinder to verify that a stack is sane. However, newly forked tasks don't always follow that convention, as reported by the following unwinder warning seen by Dave Jones: WARNING: kernel stack frame pointer at ffffc90001443f30 in kworker/u8:8:30468 has bad value (null) The warning was due to the following call chain: (ftrace handler) call_usermodehelper_exec_async+0x5/0x140 ret_from_fork+0x22/0x30 The problem is that ret_from_fork() doesn't create a stack frame before calling other functions. Fix that by carefully using the frame pointer macros. In addition to conforming to the end of stack convention, this also makes related stack traces more sensible by making it clear to the user that ret_from_fork() was involved. Reported-by:

Dave Jones <davej@codemonkey.org.uk> Signed-off-by:

Josh Poimboeuf <jpoimboe@redhat.com> Cc: Andy Lutomirski <luto@amacapital.net> 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: Dmitry Vyukov <dvyukov@google.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Miroslav Benes <mbenes@suse.cz> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/8854cdaab980e9700a81e9ebf0d4238e4bbb68ef.1483978430.git.jpoimboe@redhat.com Signed-off-by:

Ingo Molnar <mingo@kernel.org>

arch/x86/entry/entry_32.S

+11 −19

Original line number	Diff line number	Diff line
		@@ -254,23 +254,6 @@ 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.
		*
		@@ -279,15 +262,24 @@ ENDPROC(schedule_tail_wrapper)
		* edi: kernel thread arg
		*/
		ENTRY(ret_from_fork)
		call schedule_tail_wrapper
		FRAME_BEGIN /* help unwinder find end of stack */

		/*
		* schedule_tail() is asmlinkage so we have to put its 'prev' argument
		* on the stack.
		*/
		pushl %eax
		call schedule_tail
		popl %eax

		testl %ebx, %ebx
		jnz 1f /* kernel threads are uncommon */

		2:
		/* When we fork, we trace the syscall return in the child, too. */
		movl %esp, %eax
		leal FRAME_OFFSET(%esp), %eax
		call syscall_return_slowpath
		FRAME_END
		jmp restore_all

		/* kernel thread */

arch/x86/entry/entry_64.S

+7 −4

Original line number	Diff line number	Diff line
		@@ -36,6 +36,7 @@
		#include <asm/smap.h>
		#include <asm/pgtable_types.h>
		#include <asm/export.h>
		#include <asm/frame.h>
		#include <linux/err.h>

		.code64
		@@ -408,6 +409,7 @@ END(__switch_to_asm)
		* r12: kernel thread arg
		*/
		ENTRY(ret_from_fork)
		FRAME_BEGIN /* help unwinder find end of stack */
		movq %rax, %rdi
		call schedule_tail /* rdi: 'prev' task parameter */

		@@ -415,10 +417,11 @@ ENTRY(ret_from_fork)
		jnz 1f /* kernel threads are uncommon */

		2:
		movq %rsp, %rdi
		leaq FRAME_OFFSET(%rsp),%rdi /* pt_regs pointer */
		call syscall_return_slowpath /* returns with IRQs disabled */
		TRACE_IRQS_ON /* user mode is traced as IRQS on */
		SWAPGS
		FRAME_END
		jmp restore_regs_and_iret

		1:

Admin message