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 <miles.chen@mediatek.com>
Tested-by: Miles Chen <miles.chen@mediatek.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

diff --git a/arch/arm/crypto/blake2s-shash.c b/arch/arm/crypto/blake2s-shash.c
index 17c1c3bfe2f505f0eac3af720024ea608b26afc7..763c73beea2d046d10de5c22ec6195ab3591661e 100644 (file)
--- a/arch/arm/crypto/blake2s-shash.c
+++ b/arch/arm/crypto/blake2s-shash.c
@@ -13,12 +13,12 @@
 static int crypto_blake2s_update_arm(struct shash_desc *desc,
                                     const u8 *in, unsigned int inlen)
 {
-       return crypto_blake2s_update(desc, in, inlen, blake2s_compress);
+       return crypto_blake2s_update(desc, in, inlen, false);
 }
 
 static int crypto_blake2s_final_arm(struct shash_desc *desc, u8 *out)
 {
-       return crypto_blake2s_final(desc, out, blake2s_compress);
+       return crypto_blake2s_final(desc, out, false);
 }
 
 #define BLAKE2S_ALG(name, driver_name, digest_size)                    \

diff --git a/arch/x86/crypto/blake2s-shash.c b/arch/x86/crypto/blake2s-shash.c
index f9e2fecdb761b8c75b1ea2d16eefdf15fa12edcf..59ae28abe35cc196ecf9508e9f314e117931e49c 100644 (file)
--- a/arch/x86/crypto/blake2s-shash.c
+++ b/arch/x86/crypto/blake2s-shash.c
@@ -18,12 +18,12 @@
 static int crypto_blake2s_update_x86(struct shash_desc *desc,
                                     const u8 *in, unsigned int inlen)
 {
-       return crypto_blake2s_update(desc, in, inlen, blake2s_compress);
+       return crypto_blake2s_update(desc, in, inlen, false);
 }
 
 static int crypto_blake2s_final_x86(struct shash_desc *desc, u8 *out)
 {
-       return crypto_blake2s_final(desc, out, blake2s_compress);
+       return crypto_blake2s_final(desc, out, false);
 }
 
 #define BLAKE2S_ALG(name, driver_name, digest_size)                    \

diff --git a/crypto/blake2s_generic.c b/crypto/blake2s_generic.c
index 72fe480f9bd67de37747034a714379e884047e1c..5f96a21f8788311d954bed2b3fd1c969a97f7eeb 100644 (file)
--- a/crypto/blake2s_generic.c
+++ b/crypto/blake2s_generic.c
@@ -15,12 +15,12 @@
 static int crypto_blake2s_update_generic(struct shash_desc *desc,
                                         const u8 *in, unsigned int inlen)
 {
-       return crypto_blake2s_update(desc, in, inlen, blake2s_compress_generic);
+       return crypto_blake2s_update(desc, in, inlen, true);
 }
 
 static int crypto_blake2s_final_generic(struct shash_desc *desc, u8 *out)
 {
-       return crypto_blake2s_final(desc, out, blake2s_compress_generic);
+       return crypto_blake2s_final(desc, out, true);
 }
 
 #define BLAKE2S_ALG(name, driver_name, digest_size)                    \

diff --git a/include/crypto/internal/blake2s.h b/include/crypto/internal/blake2s.h
index d39cfa0d333e9282533ea8b17100c4e4c11cb3fc..52363eee2b20e6763c6b473a7137793258a8daa2 100644 (file)
--- a/include/crypto/internal/blake2s.h
+++ b/include/crypto/internal/blake2s.h
@@ -24,14 +24,11 @@ static inline void blake2s_set_lastblock(struct blake2s_state *state)
        state->f[0] = -1;
 }
 
-typedef void (*blake2s_compress_t)(struct blake2s_state *state,
-                                  const u8 *block, size_t nblocks, u32 inc);
-
 /* Helper functions for BLAKE2s shared by the library and shash APIs */
 
-static inline void __blake2s_update(struct blake2s_state *state,
-                                   const u8 *in, size_t inlen,
-                                   blake2s_compress_t compress)
+static __always_inline void
+__blake2s_update(struct blake2s_state *state, const u8 *in, size_t inlen,
+                bool force_generic)
 {
        const size_t fill = BLAKE2S_BLOCK_SIZE - state->buflen;
 
@@ -39,7 +36,12 @@ static inline void __blake2s_update(struct blake2s_state *state,
                return;
        if (inlen > fill) {
                memcpy(state->buf + state->buflen, in, fill);
-               (*compress)(state, state->buf, 1, BLAKE2S_BLOCK_SIZE);
+               if (force_generic)
+                       blake2s_compress_generic(state, state->buf, 1,
+                                                BLAKE2S_BLOCK_SIZE);
+               else
+                       blake2s_compress(state, state->buf, 1,
+                                        BLAKE2S_BLOCK_SIZE);
                state->buflen = 0;
                in += fill;
                inlen -= fill;
@@ -47,7 +49,12 @@ static inline void __blake2s_update(struct blake2s_state *state,
        if (inlen > BLAKE2S_BLOCK_SIZE) {
                const size_t nblocks = DIV_ROUND_UP(inlen, BLAKE2S_BLOCK_SIZE);
                /* Hash one less (full) block than strictly possible */
-               (*compress)(state, in, nblocks - 1, BLAKE2S_BLOCK_SIZE);
+               if (force_generic)
+                       blake2s_compress_generic(state, in, nblocks - 1,
+                                                BLAKE2S_BLOCK_SIZE);
+               else
+                       blake2s_compress(state, in, nblocks - 1,
+                                        BLAKE2S_BLOCK_SIZE);
                in += BLAKE2S_BLOCK_SIZE * (nblocks - 1);
                inlen -= BLAKE2S_BLOCK_SIZE * (nblocks - 1);
        }
@@ -55,13 +62,16 @@ static inline void __blake2s_update(struct blake2s_state *state,
        state->buflen += inlen;
 }
 
-static inline void __blake2s_final(struct blake2s_state *state, u8 *out,
-                                  blake2s_compress_t compress)
+static __always_inline void
+__blake2s_final(struct blake2s_state *state, u8 *out, bool force_generic)
 {
        blake2s_set_lastblock(state);
        memset(state->buf + state->buflen, 0,
               BLAKE2S_BLOCK_SIZE - state->buflen); /* Padding */
-       (*compress)(state, state->buf, 1, state->buflen);
+       if (force_generic)
+               blake2s_compress_generic(state, state->buf, 1, state->buflen);
+       else
+               blake2s_compress(state, state->buf, 1, state->buflen);
        cpu_to_le32_array(state->h, ARRAY_SIZE(state->h));
        memcpy(out, state->h, state->outlen);
 }
@@ -99,20 +109,20 @@ static inline int crypto_blake2s_init(struct shash_desc *desc)
 
 static inline int crypto_blake2s_update(struct shash_desc *desc,
                                        const u8 *in, unsigned int inlen,
-                                       blake2s_compress_t compress)
+                                       bool force_generic)
 {
        struct blake2s_state *state = shash_desc_ctx(desc);
 
-       __blake2s_update(state, in, inlen, compress);
+       __blake2s_update(state, in, inlen, force_generic);
        return 0;
 }
 
 static inline int crypto_blake2s_final(struct shash_desc *desc, u8 *out,
-                                      blake2s_compress_t compress)
+                                      bool force_generic)
 {
        struct blake2s_state *state = shash_desc_ctx(desc);
 
-       __blake2s_final(state, out, compress);
+       __blake2s_final(state, out, force_generic);
        return 0;
 }
 

diff --git a/lib/crypto/blake2s.c b/lib/crypto/blake2s.c
index 9364f79937b814d27f1f49d9c113048263cb322b..c71c09621c09cefcc18fc1987d81a6f1ee57fb6f 100644 (file)
--- 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);