From d337fbc4cb1ded1d58a1c4fe92aa9988d68ec1f3 Mon Sep 17 00:00:00 2001 From: Gilles Peskine Date: Tue, 14 Sep 2021 00:13:05 +0200 Subject: [PATCH] x86_64 MULADDC assembly: add missing constraints about memory MULADDC_CORE reads from (%%rsi) and writes to (%%rdi). This fragment is repeated up to 16 times, and %%rsi and %%rdi are s and d on entry respectively. Hence the complete asm statement reads 16 64-bit words from memory starting at s, and writes 16 64-bit words starting at d. Without any declaration of modified memory, Clang 12 and Clang 13 generated non-working code for mbedtls_mpi_mod_exp. The constraints make the unit tests pass with Clang 12. Signed-off-by: Gilles Peskine --- ChangeLog.d/muladdc-amd64-memory.txt | 3 +++ library/bn_mul.h | 6 +++--- 2 files changed, 6 insertions(+), 3 deletions(-) create mode 100644 ChangeLog.d/muladdc-amd64-memory.txt diff --git a/ChangeLog.d/muladdc-amd64-memory.txt b/ChangeLog.d/muladdc-amd64-memory.txt new file mode 100644 index 0000000000..1803e423d8 --- /dev/null +++ b/ChangeLog.d/muladdc-amd64-memory.txt @@ -0,0 +1,3 @@ +Bugfix + * Fix missing constraints on x86_64 assembly code for bignum multiplication + that broke some bignum operations with (at least) Clang 12. Fixes #4786. diff --git a/library/bn_mul.h b/library/bn_mul.h index 6ddffc4765..328e765008 100644 --- a/library/bn_mul.h +++ b/library/bn_mul.h @@ -225,9 +225,9 @@ "addq $8, %%rdi\n" #define MULADDC_STOP \ - : "+c" (c), "+D" (d), "+S" (s) \ - : "b" (b) \ - : "rax", "rdx", "r8" \ + : "+c" (c), "+D" (d), "+S" (s), "+m" (*(uint64_t (*)[16]) d) \ + : "b" (b), "m" (*(const uint64_t (*)[16]) s) \ + : "rax", "rdx", "r8" \ ); #endif /* AMD64 */