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x86/entry: Fix the end of the stack for newly forked tasks
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>
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2 changed files with 18 additions and 23 deletions
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@ -254,23 +254,6 @@ ENTRY(__switch_to_asm)
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jmp __switch_to
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END(__switch_to_asm)
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/*
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* The unwinder expects the last frame on the stack to always be at the same
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* offset from the end of the page, which allows it to validate the stack.
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* Calling schedule_tail() directly would break that convention because its an
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* asmlinkage function so its argument has to be pushed on the stack. This
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* wrapper creates a proper "end of stack" frame header before the call.
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*/
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ENTRY(schedule_tail_wrapper)
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FRAME_BEGIN
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pushl %eax
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call schedule_tail
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popl %eax
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FRAME_END
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ret
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ENDPROC(schedule_tail_wrapper)
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/*
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* A newly forked process directly context switches into this address.
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*
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@ -279,15 +262,24 @@ ENDPROC(schedule_tail_wrapper)
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* edi: kernel thread arg
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*/
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ENTRY(ret_from_fork)
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call schedule_tail_wrapper
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FRAME_BEGIN /* help unwinder find end of stack */
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/*
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* schedule_tail() is asmlinkage so we have to put its 'prev' argument
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* on the stack.
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*/
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pushl %eax
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call schedule_tail
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popl %eax
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testl %ebx, %ebx
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jnz 1f /* kernel threads are uncommon */
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2:
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/* When we fork, we trace the syscall return in the child, too. */
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movl %esp, %eax
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leal FRAME_OFFSET(%esp), %eax
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call syscall_return_slowpath
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FRAME_END
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jmp restore_all
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/* kernel thread */
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@ -36,6 +36,7 @@
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#include <asm/smap.h>
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#include <asm/pgtable_types.h>
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#include <asm/export.h>
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#include <asm/frame.h>
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#include <linux/err.h>
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.code64
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@ -408,17 +409,19 @@ END(__switch_to_asm)
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* r12: kernel thread arg
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*/
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ENTRY(ret_from_fork)
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FRAME_BEGIN /* help unwinder find end of stack */
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movq %rax, %rdi
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call schedule_tail /* rdi: 'prev' task parameter */
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call schedule_tail /* rdi: 'prev' task parameter */
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testq %rbx, %rbx /* from kernel_thread? */
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jnz 1f /* kernel threads are uncommon */
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testq %rbx, %rbx /* from kernel_thread? */
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jnz 1f /* kernel threads are uncommon */
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2:
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movq %rsp, %rdi
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leaq FRAME_OFFSET(%rsp),%rdi /* pt_regs pointer */
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call syscall_return_slowpath /* returns with IRQs disabled */
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TRACE_IRQS_ON /* user mode is traced as IRQS on */
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SWAPGS
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FRAME_END
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jmp restore_regs_and_iret
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1:
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