4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jann Horn jannh@google.com
commit f4f34e1b82eb4219d8eaa1c7e2e17ca219a6a2b5 upstream.
When the frame unwinder is invoked for an oops caused by a call to NULL, it currently skips the parent function because BP still points to the parent's stack frame; the (nonexistent) current function only has the first half of a stack frame, and BP doesn't point to it yet.
Add a special case for IP==0 that calculates a fake BP from SP, then uses the real BP for the next frame.
Note that this handles first_frame specially: Return information about the parent function as long as the saved IP is >=first_frame, even if the fake BP points below it.
With an artificially-added NULL call in prctl_set_seccomp(), before this patch, the trace is:
Call Trace: ? prctl_set_seccomp+0x3a/0x50 __x64_sys_prctl+0x457/0x6f0 ? __ia32_sys_prctl+0x750/0x750 do_syscall_64+0x72/0x160 entry_SYSCALL_64_after_hwframe+0x44/0xa9
After this patch, the trace is:
Call Trace: prctl_set_seccomp+0x3a/0x50 __x64_sys_prctl+0x457/0x6f0 ? __ia32_sys_prctl+0x750/0x750 do_syscall_64+0x72/0x160 entry_SYSCALL_64_after_hwframe+0x44/0xa9
Signed-off-by: Jann Horn jannh@google.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Acked-by: Josh Poimboeuf jpoimboe@redhat.com Cc: Borislav Petkov bp@alien8.de Cc: Andrew Morton akpm@linux-foundation.org Cc: syzbot syzbot+ca95b2b7aef9e7cbd6ab@syzkaller.appspotmail.com Cc: "H. Peter Anvin" hpa@zytor.com Cc: Masahiro Yamada yamada.masahiro@socionext.com Cc: Michal Marek michal.lkml@markovi.net Cc: linux-kbuild@vger.kernel.org Link: https://lkml.kernel.org/r/20190301031201.7416-1-jannh@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/include/asm/unwind.h | 6 ++++++ arch/x86/kernel/unwind_frame.c | 25 ++++++++++++++++++++++--- 2 files changed, 28 insertions(+), 3 deletions(-)
--- a/arch/x86/include/asm/unwind.h +++ b/arch/x86/include/asm/unwind.h @@ -23,6 +23,12 @@ struct unwind_state { #elif defined(CONFIG_UNWINDER_FRAME_POINTER) bool got_irq; unsigned long *bp, *orig_sp, ip; + /* + * If non-NULL: The current frame is incomplete and doesn't contain a + * valid BP. When looking for the next frame, use this instead of the + * non-existent saved BP. + */ + unsigned long *next_bp; struct pt_regs *regs; #else unsigned long *sp; --- a/arch/x86/kernel/unwind_frame.c +++ b/arch/x86/kernel/unwind_frame.c @@ -320,10 +320,14 @@ bool unwind_next_frame(struct unwind_sta }
/* Get the next frame pointer: */ - if (state->regs) + if (state->next_bp) { + next_bp = state->next_bp; + state->next_bp = NULL; + } else if (state->regs) { next_bp = (unsigned long *)state->regs->bp; - else + } else { next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task, *state->bp); + }
/* Move to the next frame if it's safe: */ if (!update_stack_state(state, next_bp)) @@ -398,6 +402,21 @@ void __unwind_start(struct unwind_state
bp = get_frame_pointer(task, regs);
+ /* + * If we crash with IP==0, the last successfully executed instruction + * was probably an indirect function call with a NULL function pointer. + * That means that SP points into the middle of an incomplete frame: + * *SP is a return pointer, and *(SP-sizeof(unsigned long)) is where we + * would have written a frame pointer if we hadn't crashed. + * Pretend that the frame is complete and that BP points to it, but save + * the real BP so that we can use it when looking for the next frame. + */ + if (regs && regs->ip == 0 && + (unsigned long *)kernel_stack_pointer(regs) >= first_frame) { + state->next_bp = bp; + bp = ((unsigned long *)kernel_stack_pointer(regs)) - 1; + } + /* Initialize stack info and make sure the frame data is accessible: */ get_stack_info(bp, state->task, &state->stack_info, &state->stack_mask); @@ -410,7 +429,7 @@ void __unwind_start(struct unwind_state */ while (!unwind_done(state) && (!on_stack(&state->stack_info, first_frame, sizeof(long)) || - state->bp < first_frame)) + (state->next_bp == NULL && state->bp < first_frame))) unwind_next_frame(state); } EXPORT_SYMBOL_GPL(__unwind_start);