linux-kernel - [PATCH] x86/kprobes: Restore BTF if the single-stepping is cancelled

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Message-Id: <160389546985.106936.12727996109376240993.stgit@devnote2>
Date:   Wed, 28 Oct 2020 23:31:10 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>, tglx@...utronix.de,
        luto@...nel.org, me@...ehuey.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
        rocallahan@...il.com, alexandre.chartre@...cle.com,
        paulmck@...nel.org, frederic@...nel.org, pbonzini@...hat.com,
        sean.j.christopherson@...el.com, pmladek@...e.com,
        joel@...lfernandes.org, rostedt@...dmis.org,
        boris.ostrovsky@...cle.com, jgross@...e.com, brgerst@...il.com,
        jpoimboe@...hat.com, daniel.thompson@...aro.org,
        julliard@...ehq.org, pgofman@...eweavers.com
Subject: [PATCH] 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@...nel.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 547c7abb39f5..39f7d8c3c064 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,