Commit-ID: acb4608ad1865a42af8e0a2db332a7c3a381e1f5
Gitweb: http://git.kernel.org/tip/acb4608ad1865a42af8e0a2db332a7c3a381e1f5
Author: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate: Thu, 20 Oct 2016 11:34:41 -0500
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Fri, 21 Oct 2016 09:26:04 +0200
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 <jpoimboe@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/e176aa9272930cd3f51fda0b94e2eae356677da4.1476973742.git.jpoimboe@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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 2221ab1..5795427 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;
--
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