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6f9885a36c
There have been some reports of "bad bp value" warnings printed by the
frame pointer unwinder:
WARNING: kernel stack regs at 000000005bac7112 in sh:1014 has bad 'bp' value 0000000000000000
This warning happens when unwinding from an interrupt in
ret_from_fork(). If entry code gets interrupted, the state of the
frame pointer (rbp) may be undefined, which can confuse the unwinder,
resulting in warnings like the above.
There's an in_entry_code() check which normally silences such
warnings for entry code. But in this case, ret_from_fork() is getting
interrupted. It recently got moved out of .entry.text, so the
in_entry_code() check no longer works.
It could be moved back into .entry.text, but that would break the
noinstr validation because of the call to schedule_tail().
Instead, initialize each new task's RBP to point to the task's entry
regs via an encoded frame pointer. That will allow the unwinder to
reach the end of the stack gracefully.
Fixes: b9f6976bfb ("x86/entry/64: Move non entry code into .text section")
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Reported-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/f366bbf5a8d02e2318ee312f738112d0af74d16f.1600103007.git.jpoimboe@redhat.com
114 lines
2.5 KiB
C
114 lines
2.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_X86_FRAME_H
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#define _ASM_X86_FRAME_H
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#include <asm/asm.h>
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/*
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* These are stack frame creation macros. They should be used by every
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* callable non-leaf asm function to make kernel stack traces more reliable.
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*/
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#ifdef CONFIG_FRAME_POINTER
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#ifdef __ASSEMBLY__
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.macro FRAME_BEGIN
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push %_ASM_BP
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_ASM_MOV %_ASM_SP, %_ASM_BP
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.endm
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.macro FRAME_END
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pop %_ASM_BP
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.endm
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#ifdef CONFIG_X86_64
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/*
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* This is a sneaky trick to help the unwinder find pt_regs on the stack. The
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* frame pointer is replaced with an encoded pointer to pt_regs. The encoding
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* is just setting the LSB, which makes it an invalid stack address and is also
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* a signal to the unwinder that it's a pt_regs pointer in disguise.
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*
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* NOTE: This macro must be used *after* PUSH_AND_CLEAR_REGS because it corrupts
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* the original rbp.
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*/
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.macro ENCODE_FRAME_POINTER ptregs_offset=0
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leaq 1+\ptregs_offset(%rsp), %rbp
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.endm
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#else /* !CONFIG_X86_64 */
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/*
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* This is a sneaky trick to help the unwinder find pt_regs on the stack. The
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* frame pointer is replaced with an encoded pointer to pt_regs. The encoding
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* is just clearing the MSB, which makes it an invalid stack address and is also
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* a signal to the unwinder that it's a pt_regs pointer in disguise.
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*
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* NOTE: This macro must be used *after* SAVE_ALL because it corrupts the
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* original ebp.
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*/
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.macro ENCODE_FRAME_POINTER
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mov %esp, %ebp
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andl $0x7fffffff, %ebp
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.endm
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#endif /* CONFIG_X86_64 */
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#else /* !__ASSEMBLY__ */
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#define FRAME_BEGIN \
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"push %" _ASM_BP "\n" \
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_ASM_MOV "%" _ASM_SP ", %" _ASM_BP "\n"
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#define FRAME_END "pop %" _ASM_BP "\n"
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#ifdef CONFIG_X86_64
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#define ENCODE_FRAME_POINTER \
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"lea 1(%rsp), %rbp\n\t"
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static inline unsigned long encode_frame_pointer(struct pt_regs *regs)
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{
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return (unsigned long)regs + 1;
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}
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#else /* !CONFIG_X86_64 */
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#define ENCODE_FRAME_POINTER \
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"movl %esp, %ebp\n\t" \
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"andl $0x7fffffff, %ebp\n\t"
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static inline unsigned long encode_frame_pointer(struct pt_regs *regs)
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{
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return (unsigned long)regs & 0x7fffffff;
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}
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#endif /* CONFIG_X86_64 */
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#endif /* __ASSEMBLY__ */
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#define FRAME_OFFSET __ASM_SEL(4, 8)
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#else /* !CONFIG_FRAME_POINTER */
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#ifdef __ASSEMBLY__
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.macro ENCODE_FRAME_POINTER ptregs_offset=0
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.endm
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#else /* !__ASSEMBLY */
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#define ENCODE_FRAME_POINTER
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static inline unsigned long encode_frame_pointer(struct pt_regs *regs)
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{
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return 0;
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}
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#endif
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#define FRAME_BEGIN
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#define FRAME_END
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#define FRAME_OFFSET 0
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#endif /* CONFIG_FRAME_POINTER */
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#endif /* _ASM_X86_FRAME_H */
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