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

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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@xxxxxxxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ross Philipson <ross.philipson@xxxxxxxxxx>
---
  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




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