From acb4608ad1865a42af8e0a2db332a7c3a381e1f5 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Thu, 20 Oct 2016 11:34:41 -0500 Subject: [PATCH] x86/unwind: Create stack frames for saved syscall registers The entry code doesn't encode the pt_regs pointer for syscalls. But the pt_regs are always at the same location, so we can add a manual check for them. A later patch prints them as part of the oops stack dump. They could be useful, for example, to determine the arguments to a system call. Signed-off-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/e176aa9272930cd3f51fda0b94e2eae356677da4.1476973742.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/unwind_frame.c | 35 ++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c index 2221ab1678c5..579542736b7e 100644 --- a/arch/x86/kernel/unwind_frame.c +++ b/arch/x86/kernel/unwind_frame.c @@ -24,6 +24,14 @@ unsigned long unwind_get_return_address(struct unwind_state *state) } EXPORT_SYMBOL_GPL(unwind_get_return_address); +static bool is_last_task_frame(struct unwind_state *state) +{ + unsigned long bp = (unsigned long)state->bp; + unsigned long regs = (unsigned long)task_pt_regs(state->task); + + return bp == regs - FRAME_HEADER_SIZE; +} + /* * This determines if the frame pointer actually contains an encoded pointer to * pt_regs on the stack. See ENCODE_FRAME_POINTER. @@ -71,6 +79,33 @@ bool unwind_next_frame(struct unwind_state *state) if (state->regs && user_mode(state->regs)) goto the_end; + if (is_last_task_frame(state)) { + regs = task_pt_regs(state->task); + + /* + * kthreads (other than the boot CPU's idle thread) have some + * partial regs at the end of their stack which were placed + * there by copy_thread_tls(). But the regs don't have any + * useful information, so we can skip them. + * + * This user_mode() check is slightly broader than a PF_KTHREAD + * check because it also catches the awkward situation where a + * newly forked kthread transitions into a user task by calling + * do_execve(), which eventually clears PF_KTHREAD. + */ + if (!user_mode(regs)) + goto the_end; + + /* + * We're almost at the end, but not quite: there's still the + * syscall regs frame. Entry code doesn't encode the regs + * pointer for syscalls, so we have to set it manually. + */ + state->regs = regs; + state->bp = NULL; + return true; + } + /* get the next frame pointer */ if (state->regs) next_bp = (unsigned long *)state->regs->bp; -- 2.20.1