[PATCH v2 42/44] entry, kasan, x86: Disallow overriding mem*() functions

Peter Zijlstra
2022-09-19T10:00:21Z

KASAN cannot just hijack the mem*() functions, it needs to emit
__asan_mem*() variants if it wants instrumentation (other sanitizers
already do this).

vmlinux.o: warning: objtool: sync_regs+0x24: call to memcpy() leaves .noinstr.text section
vmlinux.o: warning: objtool: vc_switch_off_ist+0xbe: call to memcpy() leaves .noinstr.text section
vmlinux.o: warning: objtool: fixup_bad_iret+0x36: call to memset() leaves .noinstr.text section
vmlinux.o: warning: objtool: __sev_get_ghcb+0xa0: call to memcpy() leaves .noinstr.text section
vmlinux.o: warning: objtool: __sev_put_ghcb+0x35: call to memcpy() leaves .noinstr.text section

Remove the weak aliases to ensure nobody hijacks these functions and
add them to the noinstr section.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/lib/memcpy_64.S | 5 ++---
arch/x86/lib/memmove_64.S | 4 +++-
arch/x86/lib/memset_64.S | 4 +++-
mm/kasan/kasan.h | 4 ++++
mm/kasan/shadow.c | 38 ++++++++++++++++++++++++++++++++++++++
tools/objtool/check.c | 3 +++
6 files changed, 53 insertions(+), 5 deletions(-)

--- a/arch/x86/lib/memcpy_64.S
+++ b/arch/x86/lib/memcpy_64.S
@@ -7,7 +7,7 @@
#include <asm/alternative.h>
#include <asm/export.h>

-.pushsection .noinstr.text, "ax"
+.section .noinstr.text, "ax"

/*
* We build a jump to memcpy_orig by default which gets NOPped out on
@@ -42,7 +42,7 @@ SYM_FUNC_START(__memcpy)
SYM_FUNC_END(__memcpy)
EXPORT_SYMBOL(__memcpy)

-SYM_FUNC_ALIAS_WEAK(memcpy, __memcpy)
+SYM_FUNC_ALIAS(memcpy, __memcpy)
EXPORT_SYMBOL(memcpy)

/*
@@ -183,4 +183,3 @@ SYM_FUNC_START_LOCAL(memcpy_orig)
RET
SYM_FUNC_END(memcpy_orig)

-.popsection
--- a/arch/x86/lib/memmove_64.S
+++ b/arch/x86/lib/memmove_64.S
@@ -13,6 +13,8 @@

#undef memmove

+.section .noinstr.text, "ax"
+
/*
* Implement memmove(). This can handle overlap between src and dst.
*
@@ -213,5 +215,5 @@ SYM_FUNC_START(__memmove)
SYM_FUNC_END(__memmove)
EXPORT_SYMBOL(__memmove)

-SYM_FUNC_ALIAS_WEAK(memmove, __memmove)
+SYM_FUNC_ALIAS(memmove, __memmove)
EXPORT_SYMBOL(memmove)
--- a/arch/x86/lib/memset_64.S
+++ b/arch/x86/lib/memset_64.S
@@ -6,6 +6,8 @@
#include <asm/alternative.h>
#include <asm/export.h>

+.section .noinstr.text, "ax"
+
/*
* ISO C memset - set a memory block to a byte value. This function uses fast
* string to get better performance than the original function. The code is
@@ -43,7 +45,7 @@ SYM_FUNC_START(__memset)
SYM_FUNC_END(__memset)
EXPORT_SYMBOL(__memset)

-SYM_FUNC_ALIAS_WEAK(memset, __memset)
+SYM_FUNC_ALIAS(memset, __memset)
EXPORT_SYMBOL(memset)

/*
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -551,6 +551,10 @@ void __asan_set_shadow_f3(const void *ad
void __asan_set_shadow_f5(const void *addr, size_t size);
void __asan_set_shadow_f8(const void *addr, size_t size);

+void *__asan_memset(void *addr, int c, size_t len);
+void *__asan_memmove(void *dest, const void *src, size_t len);
+void *__asan_memcpy(void *dest, const void *src, size_t len);
+
void __hwasan_load1_noabort(unsigned long addr);
void __hwasan_store1_noabort(unsigned long addr);
void __hwasan_load2_noabort(unsigned long addr);
--- a/mm/kasan/shadow.c
+++ b/mm/kasan/shadow.c
@@ -38,6 +38,12 @@ bool __kasan_check_write(const volatile
}
EXPORT_SYMBOL(__kasan_check_write);

+#ifndef CONFIG_GENERIC_ENTRY
+/*
+ * CONFIG_GENERIC_ENTRY relies on compiler emitted mem*() calls to not be
+ * instrumented. KASAN enabled toolchains should emit __asan_mem*() functions
+ * for the sites they want to instrument.
+ */
#undef memset
void *memset(void *addr, int c, size_t len)
{
@@ -68,6 +74,38 @@ void *memcpy(void *dest, const void *src

return __memcpy(dest, src, len);
}
+#endif
+
+void *__asan_memset(void *addr, int c, size_t len)
+{
+ if (!kasan_check_range((unsigned long)addr, len, true, _RET_IP_))
+ return NULL;
+
+ return __memset(addr, c, len);
+}
+EXPORT_SYMBOL(__asan_memset);
+
+#ifdef __HAVE_ARCH_MEMMOVE
+void *__asan_memmove(void *dest, const void *src, size_t len)
+{
+ if (!kasan_check_range((unsigned long)src, len, false, _RET_IP_) ||
+ !kasan_check_range((unsigned long)dest, len, true, _RET_IP_))
+ return NULL;
+
+ return __memmove(dest, src, len);
+}
+EXPORT_SYMBOL(__asan_memmove);
+#endif
+
+void *__asan_memcpy(void *dest, const void *src, size_t len)
+{
+ if (!kasan_check_range((unsigned long)src, len, false, _RET_IP_) ||
+ !kasan_check_range((unsigned long)dest, len, true, _RET_IP_))
+ return NULL;
+
+ return __memcpy(dest, src, len);
+}
+EXPORT_SYMBOL(__asan_memcpy);

void kasan_poison(const void *addr, size_t size, u8 value, bool init)
{
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -956,6 +956,9 @@ static const char *uaccess_safe_builtin[
"__asan_store16_noabort",
"__kasan_check_read",
"__kasan_check_write",
+ "__asan_memset",
+ "__asan_memmove",
+ "__asan_memcpy",
/* KASAN in-line */
"__asan_report_load_n_noabort",
"__asan_report_load1_noabort",