Commit 4a6b27b7 authored May 16, 2016 by Josh Poimboeuf Committed by Herbert Xu May 17, 2016

crypto: sha1-mb - make sha1_x8_avx2() conform to C function ABI



Megha Dey reported a kernel panic in crypto code.  The problem is that
sha1_x8_avx2() clobbers registers r12-r15 without saving and restoring
them.

Before commit aec4d0e3 ("x86/asm/crypto: Simplify stack usage in
sha-mb functions"), those registers were saved and restored by the
callers of the function.  I removed them with that commit because I
didn't realize sha1_x8_avx2() clobbered them.

Fix the potential undefined behavior associated with clobbering the
registers and make the behavior less surprising by changing the
registers to be callee saved/restored to conform with the C function
call ABI.

Also, rdx (aka RSP_SAVE) doesn't need to be saved: I verified that none
of the callers rely on it being saved, and it's not a callee-saved
register in the C ABI.

Fixes: aec4d0e3 ("x86/asm/crypto: Simplify stack usage in sha-mb functions")
Cc: stable@vger.kernel.org # 4.6
Reported-by: Megha Dey <megha.dey@linux.intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

parent 256b1cfb

arch/x86/crypto/sha-mb/sha1_x8_avx2.S

+11 −2

Original line number	Diff line number	Diff line
		@@ -296,7 +296,11 @@ W14 = TMP_
		#
		ENTRY(sha1_x8_avx2)

		push RSP_SAVE
		# save callee-saved clobbered registers to comply with C function ABI
		push %r12
		push %r13
		push %r14
		push %r15

		#save rsp
		mov %rsp, RSP_SAVE
		@@ -446,7 +450,12 @@ lloop:
		## Postamble

		mov RSP_SAVE, %rsp
		pop RSP_SAVE

		# restore callee-saved clobbered registers
		pop %r15
		pop %r14
		pop %r13
		pop %r12

		ret
		ENDPROC(sha1_x8_avx2)