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Date:   Wed,  2 Nov 2022 12:06:11 +0100
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Message-ID: <20221102110611.1085175-5-glider@google.com>
Subject: [PATCH 5/5] x86/traps: avoid KMSAN bugs originating from handle_bug()
From:   Alexander Potapenko <glider@google.com>
To:     glider@google.com
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, x86@kernel.org
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There is a case in exc_invalid_op handler that is executed outside the
irqentry_enter()/irqentry_exit() region when an UD2 instruction is used
to encode a call to __warn().

In that case the `struct pt_regs` passed to the interrupt handler is
never unpoisoned by KMSAN (this is normally done in irqentry_enter()),
which leads to false positives inside handle_bug().

Use kmsan_unpoison_entry_regs() to explicitly unpoison those registers
before using them.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86@kernel.org
Signed-off-by: Alexander Potapenko <glider@google.com>
---
 arch/x86/kernel/traps.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 178015a820f08..d3fdec706f1d2 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -15,6 +15,7 @@
 #include <linux/context_tracking.h>
 #include <linux/interrupt.h>
 #include <linux/kallsyms.h>
+#include <linux/kmsan.h>
 #include <linux/spinlock.h>
 #include <linux/kprobes.h>
 #include <linux/uaccess.h>
@@ -301,6 +302,12 @@ static noinstr bool handle_bug(struct pt_regs *regs)
 {
 	bool handled = false;
 
+	/*
+	 * Normally @regs are unpoisoned by irqentry_enter(), but handle_bug()
+	 * is a rare case that uses @regs without passing them to
+	 * irqentry_enter().
+	 */
+	kmsan_unpoison_entry_regs(regs);
 	if (!is_valid_bugaddr(regs->ip))
 		return handled;
 
-- 
2.38.1.273.g43a17bfeac-goog