linux-kernel - [PATCH v5 2/2] x86/boot: Warn on future overlapping memcpy() use

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Date:	Mon,  2 May 2016 15:51:01 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Kees Cook <keescook@...omium.org>,
	Lasse Collin <lasse.collin@...aani.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Yinghai Lu <yinghai@...nel.org>, Baoquan He <bhe@...hat.com>,
	Borislav Petkov <bp@...e.de>,
	"x86@...nel.org" <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH v5 2/2] x86/boot: Warn on future overlapping memcpy() use

If an overlapping memcpy() is ever attempted, we should at least report
it, in case it might lead to problems, so it could be changed to a
memmove() call instead.

Suggested-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/x86/boot/compressed/string.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/x86/boot/compressed/string.c b/arch/x86/boot/compressed/string.c
index faa4dc7dc66b..cea140ce6b42 100644
--- a/arch/x86/boot/compressed/string.c
+++ b/arch/x86/boot/compressed/string.c
@@ -10,7 +10,7 @@
 #include "../string.c"
 
 #ifdef CONFIG_X86_32
-void *memcpy(void *dest, const void *src, size_t n)
+static void *__memcpy(void *dest, const void *src, size_t n)
 {
 	int d0, d1, d2;
 	asm volatile(
@@ -24,7 +24,7 @@ void *memcpy(void *dest, const void *src, size_t n)
 	return dest;
 }
 #else
-void *memcpy(void *dest, const void *src, size_t n)
+static void *__memcpy(void *dest, const void *src, size_t n)
 {
 	long d0, d1, d2;
 	asm volatile(
@@ -55,10 +55,20 @@ void *memmove(void *dest, const void *src, size_t n)
 	const unsigned char *s = src;
 
 	if (d <= s || d - s >= n)
-		return memcpy(dest, src, n);
+		return __memcpy(dest, src, n);
 
 	while (n-- > 0)
 		d[n] = s[n];
 
 	return dest;
 }
+
+/* Detect and warn about potential overlaps, but handle them with memmove. */
+void *memcpy(void *dest, const void *src, size_t n)
+{
+	if (dest > src && dest - src < n) {
+		warn("Avoiding potentially unsafe overlapping memcpy()!");
+		return memmove(dest, src, n);
+	}
+	return __memcpy(dest, src, n);
+}
-- 
2.6.3