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

[ross.philipson@oracle.com]

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