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

Jarkko Sakkinen
2024-06-04T18:52:28Z

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?

> 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.

> +}
> +
> +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;

?

> + 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?

> +}
> +
> +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?

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

BR, Jarkko