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    Subject[PATCH] lib/crypto: blake2s: avoid indirect calls to compression function for Clang CFI
    Date
    blake2s_compress_generic is weakly aliased to blake2s_generic. 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")
    Reported-by: Miles Chen <miles.chen@mediatek.com>
    Cc: Nick Desaulniers <ndesaulniers@google.com>
    Cc: Sami Tolvanen <samitolvanen@google.com>
    Cc: Ard Biesheuvel <ardb@kernel.org>
    Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
    ---
    arch/arm/crypto/blake2s-shash.c | 4 ++--
    arch/x86/crypto/blake2s-shash.c | 4 ++--
    crypto/blake2s_generic.c | 4 ++--
    include/crypto/internal/blake2s.h | 36 ++++++++++++++++++-------------
    lib/crypto/blake2s.c | 4 ++--
    5 files changed, 29 insertions(+), 23 deletions(-)

    diff --git a/arch/arm/crypto/blake2s-shash.c b/arch/arm/crypto/blake2s-shash.c
    index 17c1c3bfe2f5..763c73beea2d 100644
    --- 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 f9e2fecdb761..59ae28abe35c 100644
    --- 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 72fe480f9bd6..5f96a21f8788 100644
    --- 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 d39cfa0d333e..e2da9b413d44 100644
    --- 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 +36,10 @@ 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 +47,10 @@ 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 +58,16 @@ 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 +105,20 @@ 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 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);
    --
    2.34.1
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