From 90b797f00e825c45739a8c2cf0364eb8bf5513c0 Mon Sep 17 00:00:00 2001 From: David Benjamin Date: Fri, 14 Jun 2019 17:06:52 -0400 Subject: [PATCH] Avoid leaking intermediate states in point doubling special case. Cherry picked from https://github.com/google/boringssl/commit/12d9ed670da3edd64ce8175cfe0e091982989c18 Reviewed-by: Nicola Tuveri Reviewed-by: Matt Caswell Reviewed-by: Bernd Edlinger (Merged from https://github.com/openssl/openssl/pull/9239) --- crypto/ec/asm/ecp_nistz256-x86_64.pl | 21 +++++++++++++++------ 1 file changed, 15 insertions(+), 6 deletions(-) diff --git a/crypto/ec/asm/ecp_nistz256-x86_64.pl b/crypto/ec/asm/ecp_nistz256-x86_64.pl index 97ff6fb659..cd08df9453 100755 --- a/crypto/ec/asm/ecp_nistz256-x86_64.pl +++ b/crypto/ec/asm/ecp_nistz256-x86_64.pl @@ -3628,17 +3628,26 @@ $code.=<<___; or $acc5, $acc4 # see if result is zero or $acc0, $acc4 - or $acc1, $acc4 + or $acc1, $acc4 # !is_equal(U1, U2) - .byte 0x3e # predict taken - jnz .Ladd_proceed$x # is_equal(U1,U2)? movq %xmm2, $acc0 movq %xmm3, $acc1 - test $acc0, $acc0 - jnz .Ladd_proceed$x # (in1infty || in2infty)? + + or $acc0, $acc4 + .byte 0x3e # predict taken + jnz .Ladd_proceed$x # !is_equal(U1, U2) || in1infty || in2infty + + # We now know A = B or A = -B and neither is infinity. Compare the + # y-coordinates via S1 and S2. test $acc1, $acc1 - jz .Ladd_double$x # is_equal(S1,S2)? + jz .Ladd_double$x # is_equal(S1, S2) + # A = -B, so the result is infinity. + # + # TODO: see https://github.com/google/boringssl/blob/12d9ed670da3edd64ce8175cfe0e091982989c18/crypto/fipsmodule/ec/asm/p256-x86_64-asm.pl#L3128-L3132 + # Does .Ladd_proceed handle this case? It seems to, in + # which case we should eliminate this special-case and simplify the + # timing analysis. movq %xmm0, $r_ptr # restore $r_ptr pxor %xmm0, %xmm0 movdqu %xmm0, 0x00($r_ptr) -- 2.25.1