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Commit 107101e7 authored by Jason A. Donenfeld's avatar Jason A. Donenfeld Committed by Treehugger Robot
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UPSTREAM: 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: default avatarMiles Chen <miles.chen@mediatek.com>
Tested-by: default avatarMiles Chen <miles.chen@mediatek.com>
Tested-by: default avatarNathan Chancellor <nathan@kernel.org>
Tested-by: default avatarJohn Stultz <john.stultz@linaro.org>
Acked-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Reviewed-by: default avatarEric Biggers <ebiggers@google.com>
Signed-off-by: default avatarJason A. Donenfeld <Jason@zx2c4.com>

(cherry picked from commit d2a02e3c8bb6b347818518edff5a4b40ff52d6d8)
Change-Id: I3a6461e3f05f57cd898f8a4f46e73fb0214037ef
Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
parent c3632866

arch/arm/crypto/blake2s-shash.c

+2 −2
Original line number Diff line number Diff line
@@ -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)			\

arch/x86/crypto/blake2s-shash.c

+2 −2
Original line number Diff line number Diff line
@@ -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)			\

crypto/blake2s_generic.c

+2 −2
Original line number Diff line number Diff line
@@ -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)			\

include/crypto/internal/blake2s.h

+25 −15
Original line number Diff line number Diff line
@@ -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;

}

lib/crypto/blake2s.c

+2 −2
Original line number Diff line number Diff line
@@ -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);