[PATCH 4.19 221/346] x86/kprobes: Restore BTF if the single-stepping is cancelled

Greg Kroah-Hartman
2020-12-28T16:01:31Z

From: Masami Hiramatsu <mhiramat@kernel.org>

[ Upstream commit 78ff2733ff352175eb7f4418a34654346e1b6cd2 ]

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@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/160389546985.106936.12727996109376240993.stgit@devnote2
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 07e290244ca94..dfc3ab44bc5d3 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -1041,6 +1041,11 @@ 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,
--
2.27.0