[PATCH v2] efi_loader: Change ptr arithmetics tcg eventlog buffer

[Alex G.]

Hi Ilias,

On 3/29/21 4:42 PM, Ilias Apalodimas wrote:
> Although ptr arithmetics are allowed with extensions in gcc, they
> are not allowed by the C spec. So switch to (void *)(uintptr_t) instead
> 
> Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>

Reviewed-by: Alexandru Gagniuc <mr.nuke.me at gmail.com>

> ---
> changes since v1:
> Switch over to uintptr as Alex suggested
>   lib/efi_loader/efi_tcg2.c | 19 ++++++++++---------
>   1 file changed, 10 insertions(+), 9 deletions(-)
> 
> diff --git a/lib/efi_loader/efi_tcg2.c b/lib/efi_loader/efi_tcg2.c
> index 09046844c723..ed86a220fbd6 100644
> --- a/lib/efi_loader/efi_tcg2.c
> +++ b/lib/efi_loader/efi_tcg2.c
> @@ -176,13 +176,14 @@ static efi_status_t tcg2_agile_log_append(u32 pcr_index, u32 event_type,
>   					  struct tpml_digest_values *digest_list,
>   					  u32 size, u8 event[])
>   {
> -	void *log = event_log.buffer + event_log.pos;
> +	void *log = (void *)((uintptr_t)event_log.buffer + event_log.pos);

I see two patterns here. This is the first one. If you want to dress up 
the casts, you could do:

static void *ptr_after(void *loc, size_t offset);
...

	void *log = ptr_after(event_log.buffer, event_log.pos);


>   	size_t pos;
>   	int i;
>   	u32 event_size;
>   
>   	if (event_log.get_event_called)
> -		log = event_log.final_buffer + event_log.final_pos;
> +		log = (void *)((uintptr_t)event_log.final_buffer +
> +			       event_log.final_pos);
>   
>   	/*
>   	 * size refers to the length of event[] only, we need to check against
> @@ -197,24 +198,24 @@ static efi_status_t tcg2_agile_log_append(u32 pcr_index, u32 event_type,
>   
>   	put_unaligned_le32(pcr_index, log);
>   	pos = offsetof(struct tcg_pcr_event2, event_type);
> -	put_unaligned_le32(event_type, log + pos);
> +	put_unaligned_le32(event_type, (void *)((uintptr_t)log + pos));
This is the second pattern, and I think you could improve this by doing:

static
void put_unaligned_le32_at(uint32_t val, void *base, size_t offset);
...

	put_unaligned_le32_at(event_type, log, pos);


>   	pos = offsetof(struct tcg_pcr_event2, digests); /* count */
> -	put_unaligned_le32(digest_list->count, log + pos);
> +	put_unaligned_le32(digest_list->count, (void *)((uintptr_t)log + pos));
>   
>   	pos += offsetof(struct tpml_digest_values, digests);
>   	for (i = 0; i < digest_list->count; i++) {
>   		u16 hash_alg = digest_list->digests[i].hash_alg;
>   		u8 *digest = (u8 *)&digest_list->digests[i].digest;
>   
> -		put_unaligned_le16(hash_alg, log + pos);
> +		put_unaligned_le16(hash_alg, (void *)((uintptr_t)log + pos));
>   		pos += offsetof(struct tpmt_ha, digest);
> -		memcpy(log + pos, digest, alg_to_len(hash_alg));
> +		memcpy((void *)((uintptr_t)log + pos), digest, alg_to_len(hash_alg));
>   		pos += alg_to_len(hash_alg);
>   	}
>   
> -	put_unaligned_le32(size, log + pos);
> +	put_unaligned_le32(size, (void *)((uintptr_t)log + pos));
>   	pos += sizeof(u32); /* tcg_pcr_event2 event_size*/
> -	memcpy(log + pos, event, size);
> +	memcpy((void *)((uintptr_t)log + pos), event, size);
>   	pos += size;
>   
>   	/* make sure the calculated buffer is what we checked against */
> @@ -1046,7 +1047,7 @@ static efi_status_t efi_init_event_log(void)
>   	put_unaligned_le32(0, &event_header->pcr_index);
>   	put_unaligned_le32(EV_NO_ACTION, &event_header->event_type);
>   	memset(&event_header->digest, 0, sizeof(event_header->digest));
> -	ret = create_specid_event(dev, event_log.buffer + sizeof(*event_header),
> +	ret = create_specid_event(dev, (void *)((uintptr_t)event_log.buffer + sizeof(*event_header)),
>   				  &spec_event_size);
>   	if (ret != EFI_SUCCESS)
>   		goto out;
>