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

[ 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>

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 547c7ab..39f7d8c 100644 (file)
--- 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,