[tip: perf/core] x86/kprobes: Restore BTF if the single-stepping is cancelled

[tip-bot2 for Masami Hiramatsu]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     78ff2733ff352175eb7f4418a34654346e1b6cd2
Gitweb:        https://git.kernel.org/tip/78ff2733ff352175eb7f4418a34654346e1b6cd2
Author:        Masami Hiramatsu <mhiramat@xxxxxxxxxx>
AuthorDate:    Wed, 28 Oct 2020 23:31:10 +09:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Wed, 09 Dec 2020 17:08:57 +01:00

x86/kprobes: Restore BTF if the single-stepping is cancelled

Fix to restore BTF if single-stepping causes a page fault and
it is cancelled.

Usually the BTF flag was restored when the single stepping is done
(in resume_execution()). However, if a page fault happens on the
single stepping instruction, the fault handler is invoked and
the single stepping is cancelled. Thus, the BTF flag is not
restored.

Fixes: 1ecc798c6764 ("x86: debugctlmsr kprobes")
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/160389546985.106936.12727996109376240993.stgit@devnote2
---
 arch/x86/kernel/kprobes/core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 547c7ab..39f7d8c 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -937,6 +937,11 @@ int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 		 * So clear it by resetting the current kprobe:
 		 */
 		regs->flags &= ~X86_EFLAGS_TF;
+		/*
+		 * Since the single step (trap) has been cancelled,
+		 * we need to restore BTF here.
+		 */
+		restore_btf();
 
 		/*
 		 * If the TF flag was set before the kprobe hit,