On Fri, Oct 09, 2015 at 01:18:09PM +0300, Andrey Ryabinin wrote:

2015-10-09 12:48 GMT+03:00 Mark Rutland [off-list ref]:

quoted

On Fri, Oct 09, 2015 at 12:32:18PM +0300, Andrey Ryabinin wrote:
[...]

quoted

I thought the EFI stub isolation patches create a copy of mem*() functions in the stub,
but they are just create aliases with __efistub_ prefix.

We only need to create some more aliases for KASAN.
The following patch on top of the EFI stub isolation series works for me.


Signed-off-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
---
 arch/arm64/kernel/image.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h
index e083af0..6eb8fee 100644
--- a/arch/arm64/kernel/image.h
+++ b/arch/arm64/kernel/image.h

@@ -80,6 +80,12 @@ __efistub_strcmp           = __pi_strcmp;
 __efistub_strncmp            = __pi_strncmp;
 __efistub___flush_dcache_area        = __pi___flush_dcache_area;

+#ifdef CONFIG_KASAN
+__efistub___memcpy           = __pi_memcpy;
+__efistub___memmove          = __pi_memmove;
+__efistub___memset           = __pi_memset;
+#endif

Ard's v4 stub isolation series has these aliases [1], as the stub
requires these aliases regardless of KASAN in order to link.

Stub isolation series has __efistub_memcpy, not __efistub___memcpy
(two additional '_').

Ah, I see, sorry for my sloppy reading.

The thing is, KASAN provides own implementation of memcpy() which
checks memory before access.
The original 'memcpy()' becomes __memcpy(), so we could still use it.

Ok.

In code that not instrumented by KASAN (like the EFI stub) we replace
KASAN's memcpy() with the original __mempcy():
#define memcpy() __memcpy()

I'm a little confused by this. Surely that doesn't override implicit
calls generated by the compiler, leaving us with a mixture of calls to
memcpy and __memcpy?

That doesn't matter for the stub, as both __efistub_mem* and
__efistub___mem* would point at __pe_mem*, but doesn't that matter for
other users that shouldn't be instrumented?

Is that not a problem, or do we inhibit/override that somehow?

So with CONFIG_KASAN=y the EFI stub uses __memcpy, thus we need to
create the __efistub___memcpy alias.

Ok, that makes sense to me.

Thanks,
Mark.