Re: [PATCH URGENT crypto v2] crypto: arm64/chacha - correctly walk through blocks

[Jason A. Donenfeld]

On Wed, Mar 18, 2020 at 10:25 PM Jason A. Donenfeld <Jason@xxxxxxxxx> wrote:
>
> On Wed, Mar 18, 2020 at 9:25 PM Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
> >
> > On Wed, Mar 18, 2020 at 08:27:32PM -0600, Jason A. Donenfeld wrote:
> > > It also fixes up a bug in the (optional, costly) stride test that
> > > prevented it from running on arm64.
> > [...]
> > > diff --git a/lib/crypto/chacha20poly1305-selftest.c b/lib/crypto/chacha20poly1305-selftest.c
> > > index c391a91364e9..fa43deda2660 100644
> > > --- a/lib/crypto/chacha20poly1305-selftest.c
> > > +++ b/lib/crypto/chacha20poly1305-selftest.c
> > > @@ -9028,10 +9028,15 @@ bool __init chacha20poly1305_selftest(void)
> > >            && total_len <= 1 << 10; ++total_len) {
> > >               for (i = 0; i <= total_len; ++i) {
> > >                       for (j = i; j <= total_len; ++j) {
> > > +                             k = 0;
> > >                               sg_init_table(sg_src, 3);
> > > -                             sg_set_buf(&sg_src[0], input, i);
> > > -                             sg_set_buf(&sg_src[1], input + i, j - i);
> > > -                             sg_set_buf(&sg_src[2], input + j, total_len - j);
> > > +                             if (i)
> > > +                                     sg_set_buf(&sg_src[k++], input, i);
> > > +                             if (j - i)
> > > +                                     sg_set_buf(&sg_src[k++], input + i, j - i);
> > > +                             if (total_len - j)
> > > +                                     sg_set_buf(&sg_src[k++], input + j, total_len - j);
> > > +                             sg_init_marker(sg_src, k);
> > >                               memset(computed_output, 0, total_len);
> > >                               memset(input, 0, total_len);
> >
> > So with this test fix, does this test find the bug?
>
> Yes.
>
> > Apparently the empty scatterlist elements caused some problem?  What was
> > that problem exactly?  And what do you mean by this "prevented the test
> > from running on arm64"?  If there is a problem it seems we should
> > something else about about it, e.g. debug checks that work in consistent
> > way on all architectures, documenting what the function expects, or make
> > it just work properly with empty scatterlist elements.
>
> Yea, my next plan was to look into what's going on there. In case
> you're curious, here's what happens:
>
> [    0.355761] [ffffffff041e9508] pgd=000000004ffe9003,
> pud=000000004ffe9003, pmd=0000000000000000
> [    0.356212] Internal error: Oops: 96000006 [#1] PREEMPT SMP
> [    0.356587] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 5.6.0-rc5+ #10
> [    0.356695] Hardware name: linux,dummy-virt (DT)
> [    0.356972] pstate: 20000005 (nzCv daif -PAN -UAO)
> [    0.357158] pc : scatterwalk_copychunks+0x13c/0x1e0
> [    0.357257] lr : scatterwalk_copychunks+0xe0/0x1e0
> [    0.357379] sp : ffffff800f82f970
> [    0.357450] x29: ffffff800f82f970 x28: ffffff800f838000
> [    0.357607] x27: ffffff800f838000 x26: 0000000000000001
> [    0.357725] x25: ffffff800f82faf0 x24: ffffff800f82fa10
> [    0.357820] x23: 0000000000000010 x22: 0000000000000000
> [    0.357898] x21: 0000000000000000 x20: 0000000100200000
> [    0.357978] x19: ffffff8000000000 x18: 0000000000000014
> [    0.358132] x17: 0000000000000000 x16: 0000000000000002
> [    0.358214] x15: 00000000074c5755 x14: 0000000000000002
> [    0.358310] x13: 074c57550311ac67 x12: 09579e470077af1a
> [    0.358453] x11: 1d3f98018ec6f5bb x10: 3e6144a223343e11
> [    0.358560] x9 : 0000000000000000 x8 : ffffff800f82fcc0
> [    0.358638] x7 : 0000000000000000 x6 : ffffff800fa55000
> [    0.358711] x5 : 0000000000001000 x4 : 0000000000000000
> [    0.358781] x3 : ffffffff001e9540 x2 : ffffffff001e9540
> [    0.358855] x1 : ffffffff041e9500 x0 : ffffff800f82fd60
> [    0.359007] Call trace:
> [    0.359177]  scatterwalk_copychunks+0x13c/0x1e0
> [    0.359269]  scatterwalk_map_and_copy+0x50/0xa8
> [    0.359339]  chacha20poly1305_crypt_sg_inplace+0x3f4/0x418
> [    0.359418]  chacha20poly1305_encrypt_sg_inplace+0x10/0x18
> [    0.359511]  chacha20poly1305_selftest+0x4dc/0x618
> [    0.359581]  mod_init+0xc/0x2c
> [    0.359630]  do_one_initcall+0x58/0x11c
> [    0.359687]  kernel_init_freeable+0x174/0x1e0
> [    0.359751]  kernel_init+0x10/0x100
> [    0.359803]  ret_from_fork+0x10/0x18
> [    0.360074] Code: f9400002 530c7c21 927ef442 8b011841 (f9400423)
> [    0.360257] ---[ end trace 0b64264f8a25dbdf ]---
> [    0.360453] Kernel panic - not syncing: Fatal exception
> [    0.360597] SMP: stopping secondary CPUs
> [    0.360835] Kernel Offset: disabled
> [    0.360985] CPU features: 0x00002,00002000
> [    0.361042] Memory Limit: none

__read_once_size at include/linux/compiler.h:199
(inlined by) compound_head at include/linux/page-flags.h:174
(inlined by) PageSlab at include/linux/page-flags.h:325
(inlined by) scatterwalk_pagedone at include/crypto/scatterwalk.h:88
(inlined by) scatterwalk_copychunks at crypto/scatterwalk.c:50

Bug makes sense.

scatterwalk_copychunks->scatterwalk_pagedone->PageSlab, but length
zero page means we're looking at nonsense.

So this v2 seems to be the correct fix.