From: Eric Sandeen <sandeen@xxxxxxxxxxx> Date: Thu, 1 Jun 2017 21:10:50 -0500 > On ARM, there was a gcc bug causing similar results - I /think/ > it was https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63293 > > "programs could fail sporadically with this if an interrupt happens at > the wrong instant in time and data was written onto the current stack." > > https://gcc.gnu.org/ml/gcc-patches/2014-09/msg02292.html > > Maybe totally unrelated; if not, hope it helps. :) Wow, that looks exactly like what the bug is: crc32c: .register %g2, #scratch save %sp, -176, %sp ! sethi %hi(tfm), %g1 !, tmp121 mov %i2, %o2 ! length, ldx [%g1+%lo(tfm)], %g2 ! tfm, tfm.0_4 mov %i1, %o1 ! address, lduw [%g2], %g1 ! tfm.0_4->descsize, tfm.0_4->descsize add %g1, 38, %g1 ! tfm.0_4->descsize,, tmp126 srlx %g1, 4, %g1 ! tmp126,, tmp127 sllx %g1, 4, %g1 ! tmp127,, tmp128 sub %sp, %g1, %sp !, tmp128, add %sp, 2230, %i5 !,, tmp130 Ok, %i5 holds the stack address of the shash context: ... return %i7+8 lduw [%o5+16], %o0 ! MEM[(u32 *)__shash_desc.1_10 + 16B], 'return' deallocates the stack frame plus the register window, and at the same time does a delayed control transfer to "%i7 + 8". So in the branch delay slot instruction %i5 becomes %o5. And here we are accessing deallocated stack memory in the delay slot. I'm using gcc-6.3.0 here. And indeed the following patch makes the problem go away: diff --git a/lib/libcrc32c.c b/lib/libcrc32c.c index 74a54b7..bf831e2 100644 --- a/lib/libcrc32c.c +++ b/lib/libcrc32c.c @@ -43,7 +43,7 @@ static struct crypto_shash *tfm; u32 crc32c(u32 crc, const void *address, unsigned int length) { SHASH_DESC_ON_STACK(shash, tfm); - u32 *ctx = (u32 *)shash_desc_ctx(shash); + u32 ret, *ctx = (u32 *)shash_desc_ctx(shash); int err; shash->tfm = tfm; @@ -53,7 +53,9 @@ u32 crc32c(u32 crc, const void *address, unsigned int length) err = crypto_shash_update(shash, address, length); BUG_ON(err); - return *ctx; + ret = *ctx; + barrier(); + return ret; } EXPORT_SYMBOL(crc32c); -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
