From 6f9885a36c006d798319661fa849f9c2922223b9 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Mon, 14 Sep 2020 12:04:22 -0500 Subject: x86/unwind/fp: Fix FP unwinding in ret_from_fork 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: b9f6976bfb94 ("x86/entry/64: Move non entry code into .text section") Reported-by: Naresh Kamboju Reported-by: Logan Gunthorpe Signed-off-by: Josh Poimboeuf Signed-off-by: Borislav Petkov Acked-by: Peter Zijlstra (Intel) Acked-by: Thomas Gleixner Link: https://lkml.kernel.org/r/f366bbf5a8d02e2318ee312f738112d0af74d16f.1600103007.git.jpoimboe@redhat.com --- arch/x86/include/asm/frame.h | 19 +++++++++++++++++++ arch/x86/kernel/process.c | 3 ++- 2 files changed, 21 insertions(+), 1 deletion(-) (limited to 'arch') diff --git a/arch/x86/include/asm/frame.h b/arch/x86/include/asm/frame.h index 296b346184b2..fb42659f6e98 100644 --- a/arch/x86/include/asm/frame.h +++ b/arch/x86/include/asm/frame.h @@ -60,12 +60,26 @@ #define FRAME_END "pop %" _ASM_BP "\n" #ifdef CONFIG_X86_64 + #define ENCODE_FRAME_POINTER \ "lea 1(%rsp), %rbp\n\t" + +static inline unsigned long encode_frame_pointer(struct pt_regs *regs) +{ + return (unsigned long)regs + 1; +} + #else /* !CONFIG_X86_64 */ + #define ENCODE_FRAME_POINTER \ "movl %esp, %ebp\n\t" \ "andl $0x7fffffff, %ebp\n\t" + +static inline unsigned long encode_frame_pointer(struct pt_regs *regs) +{ + return (unsigned long)regs & 0x7fffffff; +} + #endif /* CONFIG_X86_64 */ #endif /* __ASSEMBLY__ */ @@ -83,6 +97,11 @@ #define ENCODE_FRAME_POINTER +static inline unsigned long encode_frame_pointer(struct pt_regs *regs) +{ + return 0; +} + #endif #define FRAME_BEGIN diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 13ce616cc7af..ba4593a913fa 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -42,6 +42,7 @@ #include #include #include +#include #include "process.h" @@ -133,7 +134,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, unsigned long arg, fork_frame = container_of(childregs, struct fork_frame, regs); frame = &fork_frame->frame; - frame->bp = 0; + frame->bp = encode_frame_pointer(childregs); frame->ret_addr = (unsigned long) ret_from_fork; p->thread.sp = (unsigned long) fork_frame; p->thread.io_bitmap = NULL; -- cgit v1.2.3-70-g09d2