From: Josh Poimboeuf jpoimboe@redhat.com
[ Upstream commit 6f9885a36c006d798319661fa849f9c2922223b9 ]
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 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.160010300... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/include/asm/frame.h | 19 +++++++++++++++++++ arch/x86/kernel/process.c | 3 ++- 2 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/frame.h b/arch/x86/include/asm/frame.h index 296b346184b27..fb42659f6e988 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 fe67dbd76e517..bff502e779e44 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -42,6 +42,7 @@ #include <asm/spec-ctrl.h> #include <asm/io_bitmap.h> #include <asm/proto.h> +#include <asm/frame.h>
#include "process.h"
@@ -133,7 +134,7 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp, 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;