From d2a02e3c8bb6b347818518edff5a4b40ff52d6d8 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Wed, 19 Jan 2022 14:35:06 +0100 Subject: lib/crypto: blake2s: avoid indirect calls to compression function for Clang CFI blake2s_compress_generic is weakly aliased by blake2s_compress. The current harness for function selection uses a function pointer, which is ordinarily inlined and resolved at compile time. But when Clang's CFI is enabled, CFI still triggers when making an indirect call via a weak symbol. This seems like a bug in Clang's CFI, as though it's bucketing weak symbols and strong symbols differently. It also only seems to trigger when "full LTO" mode is used, rather than "thin LTO". [ 0.000000][ T0] Kernel panic - not syncing: CFI failure (target: blake2s_compress_generic+0x0/0x1444) [ 0.000000][ T0] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.16.0-mainline-06981-g076c855b846e #1 [ 0.000000][ T0] Hardware name: MT6873 (DT) [ 0.000000][ T0] Call trace: [ 0.000000][ T0] dump_backtrace+0xfc/0x1dc [ 0.000000][ T0] dump_stack_lvl+0xa8/0x11c [ 0.000000][ T0] panic+0x194/0x464 [ 0.000000][ T0] __cfi_check_fail+0x54/0x58 [ 0.000000][ T0] __cfi_slowpath_diag+0x354/0x4b0 [ 0.000000][ T0] blake2s_update+0x14c/0x178 [ 0.000000][ T0] _extract_entropy+0xf4/0x29c [ 0.000000][ T0] crng_initialize_primary+0x24/0x94 [ 0.000000][ T0] rand_initialize+0x2c/0x6c [ 0.000000][ T0] start_kernel+0x2f8/0x65c [ 0.000000][ T0] __primary_switched+0xc4/0x7be4 [ 0.000000][ T0] Rebooting in 5 seconds.. Nonetheless, the function pointer method isn't so terrific anyway, so this patch replaces it with a simple boolean, which also gets inlined away. This successfully works around the Clang bug. In general, I'm not too keen on all of the indirection involved here; it clearly does more harm than good. Hopefully the whole thing can get cleaned up down the road when lib/crypto is overhauled more comprehensively. But for now, we go with a simple bandaid. Fixes: 6048fdcc5f26 ("lib/crypto: blake2s: include as built-in") Link: https://github.com/ClangBuiltLinux/linux/issues/1567 Reported-by: Miles Chen Tested-by: Miles Chen Tested-by: Nathan Chancellor Tested-by: John Stultz Acked-by: Nick Desaulniers Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- lib/crypto/blake2s.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'lib') diff --git a/lib/crypto/blake2s.c b/lib/crypto/blake2s.c index 9364f79937b8..c71c09621c09 100644 --- a/lib/crypto/blake2s.c +++ b/lib/crypto/blake2s.c @@ -18,14 +18,14 @@ void blake2s_update(struct blake2s_state *state, const u8 *in, size_t inlen) { - __blake2s_update(state, in, inlen, blake2s_compress); + __blake2s_update(state, in, inlen, false); } EXPORT_SYMBOL(blake2s_update); void blake2s_final(struct blake2s_state *state, u8 *out) { WARN_ON(IS_ENABLED(DEBUG) && !out); - __blake2s_final(state, out, blake2s_compress); + __blake2s_final(state, out, false); memzero_explicit(state, sizeof(*state)); } EXPORT_SYMBOL(blake2s_final); -- cgit v1.2.3