Re: [PATCH v9 06/19] x86: Add early SHA-1 support for Secure Launch early measurements

ross.philipson
2024-06-04T21:03:35Z

On 6/4/24 11:52 AM, Jarkko Sakkinen wrote:
> On Fri May 31, 2024 at 4:03 AM EEST, Ross Philipson wrote:
>> From: "Daniel P. Smith" <dpsmith@apertussolutions.com>
>>
>> For better or worse, Secure Launch needs SHA-1 and SHA-256. The
>> choice of hashes used lie with the platform firmware, not with
>> software, and is often outside of the users control.
>>
>> Even if we'd prefer to use SHA-256-only, if firmware elected to start us
>> with the SHA-1 and SHA-256 backs active, we still need SHA-1 to parse
>> the TPM event log thus far, and deliberately cap the SHA-1 PCRs in order
>> to safely use SHA-256 for everything else.
>>
>> The SHA-1 code here has its origins in the code from the main kernel:
>>
>> commit c4d5b9ffa31f ("crypto: sha1 - implement base layer for SHA-1")
>>
>> A modified version of this code was introduced to the lib/crypto/sha1.c
>> to bring it in line with the SHA-256 code and allow it to be pulled into the
>> setup kernel in the same manner as SHA-256 is.
>>
>> Signed-off-by: Daniel P. Smith <dpsmith@apertussolutions.com>
>> Signed-off-by: Ross Philipson <ross.philipson@oracle.com>
>> ---
>> arch/x86/boot/compressed/Makefile | 2 +
>> arch/x86/boot/compressed/early_sha1.c | 12 ++++
>> include/crypto/sha1.h | 1 +
>> lib/crypto/sha1.c | 81 +++++++++++++++++++++++++++
>> 4 files changed, 96 insertions(+)
>> create mode 100644 arch/x86/boot/compressed/early_sha1.c
>>
>> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
>> index e9522c6893be..3307ebef4e1b 100644
>> --- a/arch/x86/boot/compressed/Makefile
>> +++ b/arch/x86/boot/compressed/Makefile
>> @@ -118,6 +118,8 @@ vmlinux-objs-$(CONFIG_EFI) += $(obj)/efi.o
>> vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_mixed.o
>> vmlinux-objs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
>>
>> +vmlinux-objs-$(CONFIG_SECURE_LAUNCH) += $(obj)/early_sha1.o
>> +
>> $(obj)/vmlinux: $(vmlinux-objs-y) FORCE
>> $(call if_changed,ld)
>>
>> diff --git a/arch/x86/boot/compressed/early_sha1.c b/arch/x86/boot/compressed/early_sha1.c
>> new file mode 100644
>> index 000000000000..8a9b904a73ab
>> --- /dev/null
>> +++ b/arch/x86/boot/compressed/early_sha1.c
>> @@ -0,0 +1,12 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (c) 2024 Apertus Solutions, LLC.
>> + */
>> +
>> +#include <linux/init.h>
>> +#include <linux/linkage.h>
>> +#include <linux/string.h>
>> +#include <asm/boot.h>
>> +#include <asm/unaligned.h>
>> +
>> +#include "../../../../lib/crypto/sha1.c"
> }
>
> Yep, make sense. Thinking only that should this be just sha1.c.
>
> Comparing this to mainly drivers/firmware/efi/tpm.c, which is not
> early_tpm.c where the early actually probably would make more sense
> than here. Here sha1 primitive is just needed.
>
> This is definitely a nitpick but why carry a prefix that is not
> that useful, right?

I am not 100% sure what you mean here, sorry. Could you clarify about
the prefix? Do you mean why did we choose early_*? There was precedent
for doing that like early_serial_console.c.

>
>> diff --git a/include/crypto/sha1.h b/include/crypto/sha1.h
>> index 044ecea60ac8..d715dd5332e1 100644
>> --- a/include/crypto/sha1.h
>> +++ b/include/crypto/sha1.h
>> @@ -42,5 +42,6 @@ extern int crypto_sha1_finup(struct shash_desc *desc, const u8 *data,
>> #define SHA1_WORKSPACE_WORDS 16
>> void sha1_init(__u32 *buf);
>> void sha1_transform(__u32 *digest, const char *data, __u32 *W);
>> +void sha1(const u8 *data, unsigned int len, u8 *out);
>>
>> #endif /* _CRYPTO_SHA1_H */
>> diff --git a/lib/crypto/sha1.c b/lib/crypto/sha1.c
>> index 1aebe7be9401..10152125b338 100644
>> --- a/lib/crypto/sha1.c
>> +++ b/lib/crypto/sha1.c
>> @@ -137,4 +137,85 @@ void sha1_init(__u32 *buf)
>> }
>> EXPORT_SYMBOL(sha1_init);
>>
>> +static void __sha1_transform(u32 *digest, const char *data)
>> +{
>> + u32 ws[SHA1_WORKSPACE_WORDS];
>> +
>> + sha1_transform(digest, data, ws);
>> +
>> + memzero_explicit(ws, sizeof(ws));
>
> For the sake of future reference I'd carry always some inline comment
> with any memzero_explicit() call site.

We can do that.

>
>> +}
>> +
>> +static void sha1_update(struct sha1_state *sctx, const u8 *data, unsigned int len)
>> +{
>> + unsigned int partial = sctx->count % SHA1_BLOCK_SIZE;
>> +
>> + sctx->count += len;
>> +
>> + if (likely((partial + len) >= SHA1_BLOCK_SIZE)) {
>
>
> if (unlikely((partial + len) < SHA1_BLOCK_SIZE))
> goto out;
>
> ?

We could do it that way. I guess it would cut down in indenting. I defer
to Daniel Smith on this...

>
>> + int blocks;
>> +
>> + if (partial) {
>> + int p = SHA1_BLOCK_SIZE - partial;
>> +
>> + memcpy(sctx->buffer + partial, data, p);
>> + data += p;
>> + len -= p;
>> +
>> + __sha1_transform(sctx->state, sctx->buffer);
>> + }
>> +
>> + blocks = len / SHA1_BLOCK_SIZE;
>> + len %= SHA1_BLOCK_SIZE;
>> +
>> + if (blocks) {
>> + while (blocks--) {
>> + __sha1_transform(sctx->state, data);
>> + data += SHA1_BLOCK_SIZE;
>> + }
>> + }
>> + partial = 0;
>> + }
>> +
>
> out:
>
>> + if (len)
>> + memcpy(sctx->buffer + partial, data, len);
>
> Why not just memcpy() unconditionally?
>

... and this.

>> +}
>> +
>> +static void sha1_final(struct sha1_state *sctx, u8 *out)
>> +{
>> + const int bit_offset = SHA1_BLOCK_SIZE - sizeof(__be64);
>> + unsigned int partial = sctx->count % SHA1_BLOCK_SIZE;
>> + __be64 *bits = (__be64 *)(sctx->buffer + bit_offset);
>> + __be32 *digest = (__be32 *)out;
>> + int i;
>> +
>> + sctx->buffer[partial++] = 0x80;
>> + if (partial > bit_offset) {
>> + memset(sctx->buffer + partial, 0x0, SHA1_BLOCK_SIZE - partial);
>> + partial = 0;
>> +
>> + __sha1_transform(sctx->state, sctx->buffer);
>> + }
>> +
>> + memset(sctx->buffer + partial, 0x0, bit_offset - partial);
>> + *bits = cpu_to_be64(sctx->count << 3);
>> + __sha1_transform(sctx->state, sctx->buffer);
>> +
>> + for (i = 0; i < SHA1_DIGEST_SIZE / sizeof(__be32); i++)
>> + put_unaligned_be32(sctx->state[i], digest++);
>> +
>> + *sctx = (struct sha1_state){};
>> +}
>> +
>> +void sha1(const u8 *data, unsigned int len, u8 *out)
>> +{
>> + struct sha1_state sctx = {0};
>> +
>> + sha1_init(sctx.state);
>> + sctx.count = 0;
>
> Hmm... so shouldn't C99 take care of this given the initialization
> above? I'm not 100% sure here. I.e. given "= {0}", shouldn't this
> already be zero?

Yes it seems so. We will look at changing that.

>
>> + sha1_update(&sctx, data, len);
>> + sha1_final(&sctx, out);
>> +}
>> +EXPORT_SYMBOL(sha1);
>> +
>> MODULE_LICENSE("GPL");
>
> BR, Jarkko

Thanks
Ross