linux-kernel - [PATCH] x86/boot: Rename overlapping memcpy() to memmove()

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Message-ID: <20160422222641.GA15276@www.outflux.net>
Date:	Fri, 22 Apr 2016 15:26:41 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Yinghai Lu <yinghai@...nel.org>, Baoquan He <bhe@...hat.com>,
	Borislav Petkov <bp@...e.de>, Ingo Molnar <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	"H.J. Lu" <hjl.tools@...il.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Andy Lutomirski <luto@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86/boot: Rename overlapping memcpy() to memmove()

Instead of having non-standard memcpy() behavior, explicitly call the new
function memmove(), make it available to the decompressors, and switch
the two overlap cases (screen scrolling and ELF parsing) to use memmove().
Additionally documents the purpose of compressed/string.c.

Suggested-by: Lasse Collin <lasse.collin@...aani.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
For tip:x86/boot, improves "x86/boot: Make memcpy() handle overlaps"
---
 arch/x86/boot/compressed/misc.c   |  6 ++++--
 arch/x86/boot/compressed/string.c | 18 ++++++++++--------
 2 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index c57d785ff955..6dde6ccdf00e 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -32,9 +32,11 @@
 #undef memcpy
 #undef memset
 #define memzero(s, n)	memset((s), 0, (n))
+#define memmove		memmove
 
 /* Functions used by the included decompressor code below. */
 static void error(char *m);
+void *memmove(void *dest, const void *src, size_t n);
 
 /*
  * This is set up by the setup-routine at boot-time
@@ -80,7 +82,7 @@ static void scroll(void)
 {
 	int i;
 
-	memcpy(vidmem, vidmem + cols * 2, (lines - 1) * cols * 2);
+	memmove(vidmem, vidmem + cols * 2, (lines - 1) * cols * 2);
 	for (i = (lines - 1) * cols * 2; i < lines * cols * 2; i += 2)
 		vidmem[i] = ' ';
 }
@@ -307,7 +309,7 @@ static void parse_elf(void *output)
 #else
 			dest = (void *)(phdr->p_paddr);
 #endif
-			memcpy(dest, output + phdr->p_offset, phdr->p_filesz);
+			memmove(dest, output + phdr->p_offset, phdr->p_filesz);
 			break;
 		default: /* Ignore other PT_* */ break;
 		}
diff --git a/arch/x86/boot/compressed/string.c b/arch/x86/boot/compressed/string.c
index 1e10e40f49dd..29b23cfabf7b 100644
--- a/arch/x86/boot/compressed/string.c
+++ b/arch/x86/boot/compressed/string.c
@@ -1,7 +1,13 @@
+/*
+ * This provides an optimized implementation of memcpy, and a simplified
+ * implementation of memset and memmove, to avoid problems with the
+ * built-in implementations when running in the restricted decompression
+ * stub environment.
+ */
 #include "../string.c"
 
 #ifdef CONFIG_X86_32
-void *__memcpy(void *dest, const void *src, size_t n)
+void *memcpy(void *dest, const void *src, size_t n)
 {
 	int d0, d1, d2;
 	asm volatile(
@@ -15,7 +21,7 @@ void *__memcpy(void *dest, const void *src, size_t n)
 	return dest;
 }
 #else
-void *__memcpy(void *dest, const void *src, size_t n)
+void *memcpy(void *dest, const void *src, size_t n)
 {
 	long d0, d1, d2;
 	asm volatile(
@@ -40,17 +46,13 @@ void *memset(void *s, int c, size_t n)
 	return s;
 }
 
-/*
- * This memcpy is overlap safe (i.e. it is memmove without conflicting
- * with other definitions of memmove from the various decompressors.
- */
-void *memcpy(void *dest, const void *src, size_t n)
+void *memmove(void *dest, const void *src, size_t n)
 {
 	unsigned char *d = dest;
 	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];
-- 
2.6.3


-- 
Kees Cook
Chrome OS & Brillo Security