[PATCH] arm64: Mitigate MTE issues with str{n}cmp()

[Robin Murphy]

As with strlen(), the patches importing the updated str{n}cmp()
implementations were originally developed and tested before the
advent of CONFIG_KASAN_HW_TAGS, and have subsequently revealed
not to be MTE-safe. Since in-kernel MTE is still a rather niche
case, let it temporarily fall back to the generic C versions for
correctness until we can figure out the best fix.

Reported-by: Branislav Rankov <branislav.rankov at arm.com>
Signed-off-by: Robin Murphy <robin.murphy at arm.com>
---
 arch/arm64/include/asm/assembler.h | 5 +++++
 arch/arm64/include/asm/string.h    | 2 ++
 arch/arm64/lib/strcmp.S            | 2 +-
 arch/arm64/lib/strncmp.S           | 2 +-
 4 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 89faca0e740d..bfa58409a4d4 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -525,6 +525,11 @@ alternative_endif
 #define EXPORT_SYMBOL_NOKASAN(name)	EXPORT_SYMBOL(name)
 #endif
 
+#ifdef CONFIG_KASAN_HW_TAGS
+#define EXPORT_SYMBOL_NOHWKASAN(name)
+#else
+#define EXPORT_SYMBOL_NOHWKASAN(name)	EXPORT_SYMBOL_NOKASAN(name)
+#endif
 	/*
 	 * Emit a 64-bit absolute little endian symbol reference in a way that
 	 * ensures that it will be resolved at build time, even when building a
diff --git a/arch/arm64/include/asm/string.h b/arch/arm64/include/asm/string.h
index 3a3264ff47b9..95f7686b728d 100644
--- a/arch/arm64/include/asm/string.h
+++ b/arch/arm64/include/asm/string.h
@@ -12,11 +12,13 @@ extern char *strrchr(const char *, int c);
 #define __HAVE_ARCH_STRCHR
 extern char *strchr(const char *, int c);
 
+#ifndef CONFIG_KASAN_HW_TAGS
 #define __HAVE_ARCH_STRCMP
 extern int strcmp(const char *, const char *);
 
 #define __HAVE_ARCH_STRNCMP
 extern int strncmp(const char *, const char *, __kernel_size_t);
+#endif
 
 #define __HAVE_ARCH_STRLEN
 extern __kernel_size_t strlen(const char *);
diff --git a/arch/arm64/lib/strcmp.S b/arch/arm64/lib/strcmp.S
index d7bee210a798..83bcad72ec97 100644
--- a/arch/arm64/lib/strcmp.S
+++ b/arch/arm64/lib/strcmp.S
@@ -173,4 +173,4 @@ L(done):
 	ret
 
 SYM_FUNC_END_PI(strcmp)
-EXPORT_SYMBOL_NOKASAN(strcmp)
+EXPORT_SYMBOL_NOHWKASAN(strcmp)
diff --git a/arch/arm64/lib/strncmp.S b/arch/arm64/lib/strncmp.S
index 48d44f7fddb1..e42bcfcd37e6 100644
--- a/arch/arm64/lib/strncmp.S
+++ b/arch/arm64/lib/strncmp.S
@@ -258,4 +258,4 @@ L(ret0):
 	ret
 
 SYM_FUNC_END_PI(strncmp)
-EXPORT_SYMBOL_NOKASAN(strncmp)
+EXPORT_SYMBOL_NOHWKASAN(strncmp)
-- 
2.21.0.dirty