2015-08-28 17:43 GMT+03:00 Matt Fleming [off-list ref]:

On Fri, 28 Aug, at 02:09:59PM, Andrey Ryabinin wrote:

quoted

In not-instrumented code KASAN replaces instrumented
memset/memcpy/memmove with not-instrumented analogues
__memset/__memcpy/__memove.
However, on x86 the EFI stub is not linked with the kernel.
It uses not-instrumented mem*() functions from
arch/x86/boot/compressed/string.c
So we don't replace them with __mem*() variants in EFI stub.

On ARM64 the EFI stub is linked with the kernel, so we should
replace mem*() functions with __mem*(), because the EFI stub
runs before KASAN sets up early shadow.

So let's move these #undef mem* into arch's asm/efi.h which is
also included by the EFI stub.

Signed-off-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
---
 arch/x86/include/asm/efi.h             | 11 +++++++++++
 drivers/firmware/efi/libstub/efistub.h |  4 ----
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 155162e..6862f11 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h

@@ -25,6 +25,17 @@
 #define EFI32_LOADER_SIGNATURE       "EL32"
 #define EFI64_LOADER_SIGNATURE       "EL64"

+/*
+ * Sometimes we may redefine memset to __memset.
+ * The EFI stub doesn't have __memset() because it's not
+ * linked with the kernel. So we should use standard
+ * memset from arch/x86/boot/compressed/string.c
+ * The same applies to memcpy and memmove.
+ */
+#undef memcpy
+#undef memset
+#undef memmove
+

I think the key piece of information missing in this comment is that
it's redefined for KASAN, right?

Right.

quoted

 #ifdef CONFIG_X86_32

diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
index e334a01..6b6548f 100644
--- a/drivers/firmware/efi/libstub/efistub.h
+++ b/drivers/firmware/efi/libstub/efistub.h

@@ -5,10 +5,6 @@
 /* error code which can't be mistaken for valid address */
 #define EFI_ERROR    (~0UL)

-#undef memcpy
-#undef memset
-#undef memmove
-
 void efi_char16_printk(efi_system_table_t *, efi_char16_t *);

 efi_status_t efi_open_volume(efi_system_table_t *sys_table_arg, void *__image,

Does this patch have any negative consequences for arm64? Can we
safely remove these #undefs without breaking the arm64 EFI stub?

The whole point of this patch is to remove these #undefs on ARM64.
Otherwise we end up calling instrumented memset, which will access to
kasan shadow,
before we set it up
So on ARM64 we should use not-instumented __memset on ARM64, iow we
need to keep #define memset __memset.

--
Matt Fleming, Intel Open Source Technology Center