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Subject[PATCH] crypto: x86/chacha - avoid sleeping under kernel_fpu_begin()
Date
From: Eric Biggers <ebiggers@google.com>

Passing atomic=true to skcipher_walk_virt() only makes the later
skcipher_walk_done() calls use atomic memory allocations, not
skcipher_walk_virt() itself. Thus, we have to move it outside of the
preemption-disabled region (kernel_fpu_begin()/kernel_fpu_end()).

(skcipher_walk_virt() only allocates memory for certain layouts of the
input scatterlist, hence why I didn't notice this earlier...)

Reported-by: syzbot+9bf843c33f782d73ae7d@syzkaller.appspotmail.com
Fixes: 4af78261870a ("crypto: x86/chacha20 - add XChaCha20 support")
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
arch/x86/crypto/chacha_glue.c | 33 ++++++++++++++++++++-------------
1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/arch/x86/crypto/chacha_glue.c b/arch/x86/crypto/chacha_glue.c
index 9b1d3fac49433..45c1c41431766 100644
--- a/arch/x86/crypto/chacha_glue.c
+++ b/arch/x86/crypto/chacha_glue.c
@@ -127,30 +127,27 @@ static void chacha_dosimd(u32 *state, u8 *dst, const u8 *src,
}
}

-static int chacha_simd_stream_xor(struct skcipher_request *req,
+static int chacha_simd_stream_xor(struct skcipher_walk *walk,
struct chacha_ctx *ctx, u8 *iv)
{
u32 *state, state_buf[16 + 2] __aligned(8);
- struct skcipher_walk walk;
int next_yield = 4096; /* bytes until next FPU yield */
- int err;
+ int err = 0;

BUILD_BUG_ON(CHACHA_STATE_ALIGN != 16);
state = PTR_ALIGN(state_buf + 0, CHACHA_STATE_ALIGN);

- err = skcipher_walk_virt(&walk, req, true);
-
crypto_chacha_init(state, ctx, iv);

- while (walk.nbytes > 0) {
- unsigned int nbytes = walk.nbytes;
+ while (walk->nbytes > 0) {
+ unsigned int nbytes = walk->nbytes;

- if (nbytes < walk.total) {
- nbytes = round_down(nbytes, walk.stride);
+ if (nbytes < walk->total) {
+ nbytes = round_down(nbytes, walk->stride);
next_yield -= nbytes;
}

- chacha_dosimd(state, walk.dst.virt.addr, walk.src.virt.addr,
+ chacha_dosimd(state, walk->dst.virt.addr, walk->src.virt.addr,
nbytes, ctx->nrounds);

if (next_yield <= 0) {
@@ -160,7 +157,7 @@ static int chacha_simd_stream_xor(struct skcipher_request *req,
next_yield = 4096;
}

- err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
+ err = skcipher_walk_done(walk, walk->nbytes - nbytes);
}

return err;
@@ -170,13 +167,18 @@ static int chacha_simd(struct skcipher_request *req)
{
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
struct chacha_ctx *ctx = crypto_skcipher_ctx(tfm);
+ struct skcipher_walk walk;
int err;

if (req->cryptlen <= CHACHA_BLOCK_SIZE || !irq_fpu_usable())
return crypto_chacha_crypt(req);

+ err = skcipher_walk_virt(&walk, req, true);
+ if (err)
+ return err;
+
kernel_fpu_begin();
- err = chacha_simd_stream_xor(req, ctx, req->iv);
+ err = chacha_simd_stream_xor(&walk, ctx, req->iv);
kernel_fpu_end();
return err;
}
@@ -185,6 +187,7 @@ static int xchacha_simd(struct skcipher_request *req)
{
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
struct chacha_ctx *ctx = crypto_skcipher_ctx(tfm);
+ struct skcipher_walk walk;
struct chacha_ctx subctx;
u32 *state, state_buf[16 + 2] __aligned(8);
u8 real_iv[16];
@@ -193,6 +196,10 @@ static int xchacha_simd(struct skcipher_request *req)
if (req->cryptlen <= CHACHA_BLOCK_SIZE || !irq_fpu_usable())
return crypto_xchacha_crypt(req);

+ err = skcipher_walk_virt(&walk, req, true);
+ if (err)
+ return err;
+
BUILD_BUG_ON(CHACHA_STATE_ALIGN != 16);
state = PTR_ALIGN(state_buf + 0, CHACHA_STATE_ALIGN);
crypto_chacha_init(state, ctx, req->iv);
@@ -204,7 +211,7 @@ static int xchacha_simd(struct skcipher_request *req)

memcpy(&real_iv[0], req->iv + 24, 8);
memcpy(&real_iv[8], req->iv + 16, 8);
- err = chacha_simd_stream_xor(req, &subctx, real_iv);
+ err = chacha_simd_stream_xor(&walk, &subctx, real_iv);

kernel_fpu_end();

--
2.19.2
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