Subject: Re: [PATCH] crypto: vmx - Fix sleep-in-atomic bugs

From: Marcelo Henrique Cerri <[email-masked]>
Date: Tue, 21 Aug 2018 13:41:26 -0300

On Tue, Aug 21, 2018 at 05:24:45PM +0200, Ondrej Mosnáček wrote:
> CC: Paulo Flabiano Smorigo <[email-masked]>,
> [email-masked]
> 
> (Sorry, sent this before reading new e-mails in the thread...)
> 
> ut 21. 8. 2018 o 17:18 Ondrej Mosnacek <[email-masked]> napísal(a):
> >
> > This patch fixes sleep-in-atomic bugs in AES-CBC and AES-XTS VMX
> > implementations. The problem is that the blkcipher_* functions should
> > not be called in atomic context.
> >
> > The bugs can be reproduced via the AF_ALG interface by trying to
> > encrypt/decrypt sufficiently large buffers (at least 64 KiB) using the
> > VMX implementations of 'cbc(aes)' or 'xts(aes)'. Such operations then
> > trigger BUG in crypto_yield():
> >
> > [  891.863680] BUG: sleeping function called from invalid context at include/crypto/algapi.h:424
> > [  891.864622] in_atomic(): 1, irqs_disabled(): 0, pid: 12347, name: kcapi-enc
> > [  891.864739] 1 lock held by kcapi-enc/12347:
> > [  891.864811]  #0: 00000000f5d42c46 (sk_lock-AF_ALG){+.+.}, at: skcipher_recvmsg+0x50/0x530
> > [  891.865076] CPU: 5 PID: 12347 Comm: kcapi-enc Not tainted 4.19.0-0.rc0.git3.1.fc30.ppc64le #1
> > [  891.865251] Call Trace:
> > [  891.865340] [c0000003387578c0] [c000000000d67ea4] dump_stack+0xe8/0x164 (unreliable)
> > [  891.865511] [c000000338757910] [c000000000172a58] ___might_sleep+0x2f8/0x310
> > [  891.865679] [c000000338757990] [c0000000006bff74] blkcipher_walk_done+0x374/0x4a0
> > [  891.865825] [c0000003387579e0] [d000000007e73e70] p8_aes_cbc_encrypt+0x1c8/0x260 [vmx_crypto]
> > [  891.865993] [c000000338757ad0] [c0000000006c0ee0] skcipher_encrypt_blkcipher+0x60/0x80
> > [  891.866128] [c000000338757b10] [c0000000006ec504] skcipher_recvmsg+0x424/0x530
> > [  891.866283] [c000000338757bd0] [c000000000b00654] sock_recvmsg+0x74/0xa0
> > [  891.866403] [c000000338757c10] [c000000000b00f64] ___sys_recvmsg+0xf4/0x2f0
> > [  891.866515] [c000000338757d90] [c000000000b02bb8] __sys_recvmsg+0x68/0xe0
> > [  891.866631] [c000000338757e30] [c00000000000bbe4] system_call+0x5c/0x70
> >
> > Fixes: 8c755ace357c ("crypto: vmx - Adding CBC routines for VMX module")
> > Fixes: c07f5d3da643 ("crypto: vmx - Adding support for XTS")
> > Cc: [email-masked]
> > Signed-off-by: Ondrej Mosnacek <[email-masked]>
> > ---
> > This patch should fix the issue, but I didn't test it. (I'll see if I
> > can find some time tomorrow to try and recompile the kernel on a PPC
> > machine... in the meantime please review :)
> >
> >  drivers/crypto/vmx/aes_cbc.c | 30 ++++++++++++++----------------
> >  drivers/crypto/vmx/aes_xts.c | 19 ++++++++++++-------
> >  2 files changed, 26 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/crypto/vmx/aes_cbc.c b/drivers/crypto/vmx/aes_cbc.c
> > index 5285ece4f33a..b71895871be3 100644
> > --- a/drivers/crypto/vmx/aes_cbc.c
> > +++ b/drivers/crypto/vmx/aes_cbc.c
> > @@ -107,24 +107,23 @@ static int p8_aes_cbc_encrypt(struct blkcipher_desc *desc,
> >                 ret = crypto_skcipher_encrypt(req);
> >                 skcipher_request_zero(req);
> >         } else {
> > -               preempt_disable();
> > -               pagefault_disable();
> > -               enable_kernel_vsx();
> > -
> >                 blkcipher_walk_init(&walk, dst, src, nbytes);
> >                 ret = blkcipher_walk_virt(desc, &walk);
> >                 while ((nbytes = walk.nbytes)) {
> > +                       preempt_disable();
> > +                       pagefault_disable();
> > +                       enable_kernel_vsx();
> >                         aes_p8_cbc_encrypt(walk.src.virt.addr,
> >                                            walk.dst.virt.addr,
> >                                            nbytes & AES_BLOCK_MASK,
> >                                            &ctx->enc_key, walk.iv, 1);
> > +                       disable_kernel_vsx();
> > +                       pagefault_enable();
> > +                       preempt_enable();
> > +
> >                         nbytes &= AES_BLOCK_SIZE - 1;
> >                         ret = blkcipher_walk_done(desc, &walk, nbytes);
> >                 }
> > -
> > -               disable_kernel_vsx();
> > -               pagefault_enable();
> > -               preempt_enable();
> >         }
> >
> >         return ret;
> > @@ -147,24 +146,23 @@ static int p8_aes_cbc_decrypt(struct blkcipher_desc *desc,
> >                 ret = crypto_skcipher_decrypt(req);
> >                 skcipher_request_zero(req);
> >         } else {
> > -               preempt_disable();
> > -               pagefault_disable();
> > -               enable_kernel_vsx();
> > -
> >                 blkcipher_walk_init(&walk, dst, src, nbytes);
> >                 ret = blkcipher_walk_virt(desc, &walk);
> >                 while ((nbytes = walk.nbytes)) {
> > +                       preempt_disable();
> > +                       pagefault_disable();
> > +                       enable_kernel_vsx();
> >                         aes_p8_cbc_encrypt(walk.src.virt.addr,
> >                                            walk.dst.virt.addr,
> >                                            nbytes & AES_BLOCK_MASK,
> >                                            &ctx->dec_key, walk.iv, 0);
> > +                       disable_kernel_vsx();
> > +                       pagefault_enable();
> > +                       preempt_enable();
> > +
> >                         nbytes &= AES_BLOCK_SIZE - 1;
> >                         ret = blkcipher_walk_done(desc, &walk, nbytes);
> >                 }
> > -
> > -               disable_kernel_vsx();
> > -               pagefault_enable();
> > -               preempt_enable();
> >         }
> >
> >         return ret;
> > diff --git a/drivers/crypto/vmx/aes_xts.c b/drivers/crypto/vmx/aes_xts.c
> > index 8bd9aff0f55f..016ef52390c9 100644
> > --- a/drivers/crypto/vmx/aes_xts.c
> > +++ b/drivers/crypto/vmx/aes_xts.c
> > @@ -116,13 +116,14 @@ static int p8_aes_xts_crypt(struct blkcipher_desc *desc,
> >                 ret = enc? crypto_skcipher_encrypt(req) : crypto_skcipher_decrypt(req);
> >                 skcipher_request_zero(req);
> >         } else {
> > +               blkcipher_walk_init(&walk, dst, src, nbytes);
> > +
> > +               ret = blkcipher_walk_virt(desc, &walk);
> > +
> >                 preempt_disable();
> >                 pagefault_disable();
> >                 enable_kernel_vsx();
> >
> > -               blkcipher_walk_init(&walk, dst, src, nbytes);
> > -
> > -               ret = blkcipher_walk_virt(desc, &walk);
> >                 iv = walk.iv;
> >                 memset(tweak, 0, AES_BLOCK_SIZE);
> >                 aes_p8_encrypt(iv, tweak, &ctx->tweak_key);
> > @@ -135,13 +136,17 @@ static int p8_aes_xts_crypt(struct blkcipher_desc *desc,
> >                                 aes_p8_xts_decrypt(walk.src.virt.addr, walk.dst.virt.addr,
> >                                                 nbytes & AES_BLOCK_MASK, &ctx->dec_key, NULL, tweak);
> >
> > +                       disable_kernel_vsx();
> > +                       pagefault_enable();
> > +                       preempt_enable();
> > +
> >                         nbytes &= AES_BLOCK_SIZE - 1;
> >                         ret = blkcipher_walk_done(desc, &walk, nbytes);
> > -               }
> >
> > -               disable_kernel_vsx();
> > -               pagefault_enable();
> > -               preempt_enable();
> > +                       preempt_disable();
> > +                       pagefault_disable();
> > +                       enable_kernel_vsx();
> > +               }

That doesn't seem right. It would leave preemption disabled when
leaving the function.

> >         }
> >         return ret;
> >  }
> > --
> > 2.17.1

--
Regards,
Marcelo