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Re: [Qemu-devel] [PATCH] target-arm: crypto: fix BE host support
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From: |
Ard Biesheuvel |
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Subject: |
Re: [Qemu-devel] [PATCH] target-arm: crypto: fix BE host support |
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Date: |
Fri, 2 Jan 2015 19:21:53 +0000 |
On 2 January 2015 at 15:17, Laszlo Ersek <address@hidden> wrote:
> On 01/02/15 15:18, Ard Biesheuvel wrote:
>> The crypto emulation code in target-arm/crypto_helper.c never worked
>> correctly on big endian hosts, due to the fact that it uses a union
>> of array types to convert between the native VFP register size (64
>> bits) and the types used in the algorithms (bytes and 32 bit words)
>>
>> We cannot just swab between LE and BE when reading and writing the
>> registers, as the SHA code performs word additions, so instead, add
>> array accessors for the CRYPTO_STATE type whose LE and BE specific
>> implementations ensure that the correct array elements are referenced.
>>
>> Signed-off-by: Ard Biesheuvel <address@hidden>
>> ---
>>
>> Only tested on a LE (amd64) host, as I don't have access to a BE host.
>>
>> target-arm/crypto_helper.c | 114
>> +++++++++++++++++++++++++--------------------
>> 1 file changed, 63 insertions(+), 51 deletions(-)
>>
>> diff --git a/target-arm/crypto_helper.c b/target-arm/crypto_helper.c
>> index dd60d0b81a4c..1fe975d0f1e3 100644
>> --- a/target-arm/crypto_helper.c
>> +++ b/target-arm/crypto_helper.c
>> @@ -22,6 +22,14 @@ union CRYPTO_STATE {
>> uint64_t l[2];
>> };
>>
>> +#ifdef HOST_WORDS_BIGENDIAN
>> +#define CR_ST_BYTE(state, i) (state.bytes[(15 - (i)) ^ 8])
>
> Produces
>
> 7, 6, 5, 4, 3, 2, 1, 0,
> 15, 14, 13, 12, 11, 10, 9
>
> which I think is consistent with what Peter wrote.
>
>> +#define CR_ST_WORD(state, i) (state.words[(3 - (i)) ^ 2])
>
> Hm. The indices look good:
>
> 1, 0
> 3, 2
>
> But, assuming you're on a big-endian host, perhaps you should byte swap
> the uint32_t too?...
>
No, I don't think so. I even removed the cpu_to_le32() call from the
aesmc helper because the MixColumns lookup tables will be emitted in
host native endianness, and the vfp.regs[] array is host native
endianness as well. I think the union type may have been a mistake to
begin with, because it introduces endianness dependencies that don't
actually exist in the code. It probably would have been cleaner if I
had defined the relation between VFP D-regs, words and bytes in terms
of shifts and masks instead.
>> (ie if you store 0x112233445566778899aabbccddeeff00 as a 64 bit write
>> to VFP register D0 then regs[0] will be
>> 0x112233445566778899aabbccddeeff00 regardless of host endianness. That
>> is, the least significant 8 bits of D0 will be (regs[0] & 0xff). (This
>> isn't the same number as if you do the union-type-punning thing with
>> union { uint64_t l; uint8_t b[8]; } and look at b[0].)
>
> Assume the guest writes value 0x112233445566778899aabbccddeeff00 (LE
> representation).
>
> * Assuming a little endian host, we get:
>
> [00 ff ee dd cc bb aa 99 88 77 66 55 44 33 22 11]
>
> (full 128-bit LE vector).
>
> This is grouped into units of four bytes for the words array:
>
> [00 ff ee dd] [cc bb aa 99] [88 77 66 55] [44 33 22 11]
>
> And the meaning of the individual uint32_t's is:
>
> 0xddeeff00 0x99aabbcc 0x55667788 0x11223344
>
> Which are the building blocks for the crypto primitives.
>
> * Assuming a big endian host, you get the following byte array for the
> same store (if I understand Peter right -- two uint64_t values are
> encoded as host endian, but the ordering between those remains little
> endian):
>
> [99 aa bb cc dd ee ff 00 11 22 33 44 55 66 77 88]
>
> (and your CR_ST_BYTE() macro looks right for this).
>
> Grouping this into units of four bytes for the words array, we get
>
> [99 aa bb cc] [dd ee ff 00] [11 22 33 44] [55 66 77 88]
>
> resulting in values
>
> 0x99aabbcc 0xddeeff00 0x11223344 0x55667788
>
> And then your CR_ST_WORD macro permutes them (1, 0, 3, 2) to the
> following values:
>
> 0xddeeff00 0x99aabbcc 0x55667788 0x11223344
>
> ... Which is identical to the LE host result.
>
> So this part looks fine to me.
>
Thanks for the elaborate review.
> Regarding the rest -- in my opinion, getting the implementation of
> crypto primitivies *wrong* despite them succesfully passing an extensive
> test suite is exceedingly unlikely. You usually cannot get crypto
> primitives "halfway right" -- as long as you don't *combine* them to
> bigger building blocks, crypto primitives are 100% specified and there
> are no "corner cases" that are usual for other program logic. The
> implementation either works or is catastrophically broken (which is
> quickly visible).
>
> Hence, if Peter gets good test results for this patchset, then I think
> that *suffices* to apply the patch.
>
Agreed.
> ... Which is why I won't try to eyeball the rest of the patch where you
> put the macros to use. :) The macros themselves are sound. If you broke
> their application, they won't pass the test suite (in the kernel bootup
> code, or elsewhere).
>
> Acked-by: Laszlo Ersek <address@hidden>
>
> Thanks
> Laszlo
>
Cheers,
Ard.
>> +#else
>> +#define CR_ST_BYTE(state, i) (state.bytes[i])
>> +#define CR_ST_WORD(state, i) (state.words[i])
>> +#endif
>> +
>> void HELPER(crypto_aese)(CPUARMState *env, uint32_t rd, uint32_t rm,
>> uint32_t decrypt)
>> {
>> @@ -46,7 +54,7 @@ void HELPER(crypto_aese)(CPUARMState *env, uint32_t rd,
>> uint32_t rm,
>>
>> /* combine ShiftRows operation and sbox substitution */
>> for (i = 0; i < 16; i++) {
>> - st.bytes[i] = sbox[decrypt][rk.bytes[shift[decrypt][i]]];
>> + CR_ST_BYTE(st, i) = sbox[decrypt][CR_ST_BYTE(rk,
>> shift[decrypt][i])];
>> }
>>
>> env->vfp.regs[rd] = make_float64(st.l[0]);
>> @@ -198,11 +206,11 @@ void HELPER(crypto_aesmc)(CPUARMState *env, uint32_t
>> rd, uint32_t rm,
>> assert(decrypt < 2);
>>
>> for (i = 0; i < 16; i += 4) {
>> - st.words[i >> 2] = cpu_to_le32(
>> - mc[decrypt][st.bytes[i]] ^
>> - rol32(mc[decrypt][st.bytes[i + 1]], 8) ^
>> - rol32(mc[decrypt][st.bytes[i + 2]], 16) ^
>> - rol32(mc[decrypt][st.bytes[i + 3]], 24));
>> + CR_ST_WORD(st, i >> 2) =
>> + mc[decrypt][CR_ST_BYTE(st, i)] ^
>> + rol32(mc[decrypt][CR_ST_BYTE(st, i + 1)], 8) ^
>> + rol32(mc[decrypt][CR_ST_BYTE(st, i + 2)], 16) ^
>> + rol32(mc[decrypt][CR_ST_BYTE(st, i + 3)], 24);
>> }
>>
>> env->vfp.regs[rd] = make_float64(st.l[0]);
>> @@ -255,24 +263,25 @@ void HELPER(crypto_sha1_3reg)(CPUARMState *env,
>> uint32_t rd, uint32_t rn,
>>
>> switch (op) {
>> case 0: /* sha1c */
>> - t = cho(d.words[1], d.words[2], d.words[3]);
>> + t = cho(CR_ST_WORD(d, 1), CR_ST_WORD(d, 2), CR_ST_WORD(d,
>> 3));
>> break;
>> case 1: /* sha1p */
>> - t = par(d.words[1], d.words[2], d.words[3]);
>> + t = par(CR_ST_WORD(d, 1), CR_ST_WORD(d, 2), CR_ST_WORD(d,
>> 3));
>> break;
>> case 2: /* sha1m */
>> - t = maj(d.words[1], d.words[2], d.words[3]);
>> + t = maj(CR_ST_WORD(d, 1), CR_ST_WORD(d, 2), CR_ST_WORD(d,
>> 3));
>> break;
>> default:
>> g_assert_not_reached();
>> }
>> - t += rol32(d.words[0], 5) + n.words[0] + m.words[i];
>> -
>> - n.words[0] = d.words[3];
>> - d.words[3] = d.words[2];
>> - d.words[2] = ror32(d.words[1], 2);
>> - d.words[1] = d.words[0];
>> - d.words[0] = t;
>> + t += rol32(CR_ST_WORD(d, 0), 5) + CR_ST_WORD(n, 0)
>> + + CR_ST_WORD(m, i);
>> +
>> + CR_ST_WORD(n, 0) = CR_ST_WORD(d, 3);
>> + CR_ST_WORD(d, 3) = CR_ST_WORD(d, 2);
>> + CR_ST_WORD(d, 2) = ror32(CR_ST_WORD(d, 1), 2);
>> + CR_ST_WORD(d, 1) = CR_ST_WORD(d, 0);
>> + CR_ST_WORD(d, 0) = t;
>> }
>> }
>> env->vfp.regs[rd] = make_float64(d.l[0]);
>> @@ -286,8 +295,8 @@ void HELPER(crypto_sha1h)(CPUARMState *env, uint32_t rd,
>> uint32_t rm)
>> float64_val(env->vfp.regs[rm + 1])
>> } };
>>
>> - m.words[0] = ror32(m.words[0], 2);
>> - m.words[1] = m.words[2] = m.words[3] = 0;
>> + CR_ST_WORD(m, 0) = ror32(CR_ST_WORD(m, 0), 2);
>> + CR_ST_WORD(m, 1) = CR_ST_WORD(m, 2) = CR_ST_WORD(m, 3) = 0;
>>
>> env->vfp.regs[rd] = make_float64(m.l[0]);
>> env->vfp.regs[rd + 1] = make_float64(m.l[1]);
>> @@ -304,10 +313,10 @@ void HELPER(crypto_sha1su1)(CPUARMState *env, uint32_t
>> rd, uint32_t rm)
>> float64_val(env->vfp.regs[rm + 1])
>> } };
>>
>> - d.words[0] = rol32(d.words[0] ^ m.words[1], 1);
>> - d.words[1] = rol32(d.words[1] ^ m.words[2], 1);
>> - d.words[2] = rol32(d.words[2] ^ m.words[3], 1);
>> - d.words[3] = rol32(d.words[3] ^ d.words[0], 1);
>> + CR_ST_WORD(d, 0) = rol32(CR_ST_WORD(d, 0) ^ CR_ST_WORD(m, 1), 1);
>> + CR_ST_WORD(d, 1) = rol32(CR_ST_WORD(d, 1) ^ CR_ST_WORD(m, 2), 1);
>> + CR_ST_WORD(d, 2) = rol32(CR_ST_WORD(d, 2) ^ CR_ST_WORD(m, 3), 1);
>> + CR_ST_WORD(d, 3) = rol32(CR_ST_WORD(d, 3) ^ CR_ST_WORD(d, 0), 1);
>>
>> env->vfp.regs[rd] = make_float64(d.l[0]);
>> env->vfp.regs[rd + 1] = make_float64(d.l[1]);
>> @@ -356,20 +365,22 @@ void HELPER(crypto_sha256h)(CPUARMState *env, uint32_t
>> rd, uint32_t rn,
>> int i;
>>
>> for (i = 0; i < 4; i++) {
>> - uint32_t t = cho(n.words[0], n.words[1], n.words[2]) + n.words[3]
>> - + S1(n.words[0]) + m.words[i];
>> -
>> - n.words[3] = n.words[2];
>> - n.words[2] = n.words[1];
>> - n.words[1] = n.words[0];
>> - n.words[0] = d.words[3] + t;
>> -
>> - t += maj(d.words[0], d.words[1], d.words[2]) + S0(d.words[0]);
>> -
>> - d.words[3] = d.words[2];
>> - d.words[2] = d.words[1];
>> - d.words[1] = d.words[0];
>> - d.words[0] = t;
>> + uint32_t t = cho(CR_ST_WORD(n, 0), CR_ST_WORD(n, 1), CR_ST_WORD(n,
>> 2))
>> + + CR_ST_WORD(n, 3) + S1(CR_ST_WORD(n, 0))
>> + + CR_ST_WORD(m, i);
>> +
>> + CR_ST_WORD(n, 3) = CR_ST_WORD(n, 2);
>> + CR_ST_WORD(n, 2) = CR_ST_WORD(n, 1);
>> + CR_ST_WORD(n, 1) = CR_ST_WORD(n, 0);
>> + CR_ST_WORD(n, 0) = CR_ST_WORD(d, 3) + t;
>> +
>> + t += maj(CR_ST_WORD(d, 0), CR_ST_WORD(d, 1), CR_ST_WORD(d, 2))
>> + + S0(CR_ST_WORD(d, 0));
>> +
>> + CR_ST_WORD(d, 3) = CR_ST_WORD(d, 2);
>> + CR_ST_WORD(d, 2) = CR_ST_WORD(d, 1);
>> + CR_ST_WORD(d, 1) = CR_ST_WORD(d, 0);
>> + CR_ST_WORD(d, 0) = t;
>> }
>>
>> env->vfp.regs[rd] = make_float64(d.l[0]);
>> @@ -394,13 +405,14 @@ void HELPER(crypto_sha256h2)(CPUARMState *env,
>> uint32_t rd, uint32_t rn,
>> int i;
>>
>> for (i = 0; i < 4; i++) {
>> - uint32_t t = cho(d.words[0], d.words[1], d.words[2]) + d.words[3]
>> - + S1(d.words[0]) + m.words[i];
>> -
>> - d.words[3] = d.words[2];
>> - d.words[2] = d.words[1];
>> - d.words[1] = d.words[0];
>> - d.words[0] = n.words[3 - i] + t;
>> + uint32_t t = cho(CR_ST_WORD(d, 0), CR_ST_WORD(d, 1), CR_ST_WORD(d,
>> 2))
>> + + CR_ST_WORD(d, 3) + S1(CR_ST_WORD(d, 0))
>> + + CR_ST_WORD(m, i);
>> +
>> + CR_ST_WORD(d, 3) = CR_ST_WORD(d, 2);
>> + CR_ST_WORD(d, 2) = CR_ST_WORD(d, 1);
>> + CR_ST_WORD(d, 1) = CR_ST_WORD(d, 0);
>> + CR_ST_WORD(d, 0) = CR_ST_WORD(n, 3 - i) + t;
>> }
>>
>> env->vfp.regs[rd] = make_float64(d.l[0]);
>> @@ -418,10 +430,10 @@ void HELPER(crypto_sha256su0)(CPUARMState *env,
>> uint32_t rd, uint32_t rm)
>> float64_val(env->vfp.regs[rm + 1])
>> } };
>>
>> - d.words[0] += s0(d.words[1]);
>> - d.words[1] += s0(d.words[2]);
>> - d.words[2] += s0(d.words[3]);
>> - d.words[3] += s0(m.words[0]);
>> + CR_ST_WORD(d, 0) += s0(CR_ST_WORD(d, 1));
>> + CR_ST_WORD(d, 1) += s0(CR_ST_WORD(d, 2));
>> + CR_ST_WORD(d, 2) += s0(CR_ST_WORD(d, 3));
>> + CR_ST_WORD(d, 3) += s0(CR_ST_WORD(m, 0));
>>
>> env->vfp.regs[rd] = make_float64(d.l[0]);
>> env->vfp.regs[rd + 1] = make_float64(d.l[1]);
>> @@ -443,10 +455,10 @@ void HELPER(crypto_sha256su1)(CPUARMState *env,
>> uint32_t rd, uint32_t rn,
>> float64_val(env->vfp.regs[rm + 1])
>> } };
>>
>> - d.words[0] += s1(m.words[2]) + n.words[1];
>> - d.words[1] += s1(m.words[3]) + n.words[2];
>> - d.words[2] += s1(d.words[0]) + n.words[3];
>> - d.words[3] += s1(d.words[1]) + m.words[0];
>> + CR_ST_WORD(d, 0) += s1(CR_ST_WORD(m, 2)) + CR_ST_WORD(n, 1);
>> + CR_ST_WORD(d, 1) += s1(CR_ST_WORD(m, 3)) + CR_ST_WORD(n, 2);
>> + CR_ST_WORD(d, 2) += s1(CR_ST_WORD(d, 0)) + CR_ST_WORD(n, 3);
>> + CR_ST_WORD(d, 3) += s1(CR_ST_WORD(d, 1)) + CR_ST_WORD(m, 0);
>>
>> env->vfp.regs[rd] = make_float64(d.l[0]);
>> env->vfp.regs[rd + 1] = make_float64(d.l[1]);
>>
>