Re: [PATCH v2 4/7] soc: qcom: mdt_loader: Enhance split binary detection

[Bjorn Andersson]

On Mon, Mar 06, 2023 at 03:11:59PM -0800, Melody Olvera wrote:
> From: Gokul Krishna Krishnakumar <quic_gokukris@xxxxxxxxxxx>
> 
> When booting with split binaries, it may be that the offset of the first
> program header lies inside the mdt's filesize, in this case the loader
> would incorrectly assume that the bins were not split. The loading would
> then continue on and fail for split bins.

Can you please be more explicit about the scenario you're having
problems with?

Is the problem that the first segment is represented in both the .mdt
and .b01, but different? Or is it that you find the hash in both .mdt
abd .b01, but only one of them is valid?

> This change updates the logic used
> by the mdt loader to understand whether the firmware images are split or not
> by checking if each programs header's segment lies within the file or not.
> 
> Signed-off-by: Gokul Krishna Krishnakumar <quic_gokukris@xxxxxxxxxxx>
> Signed-off-by: Melody Olvera <quic_molvera@xxxxxxxxxxx>
> ---
>  drivers/soc/qcom/mdt_loader.c | 64 +++++++++++++++++++----------------
>  1 file changed, 35 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/soc/qcom/mdt_loader.c b/drivers/soc/qcom/mdt_loader.c
> index 33dd8c315eb7..3aadce299c02 100644
> --- a/drivers/soc/qcom/mdt_loader.c
> +++ b/drivers/soc/qcom/mdt_loader.c
> @@ -31,6 +31,26 @@ static bool mdt_phdr_valid(const struct elf32_phdr *phdr)
>  	return true;
>  }
>  
> +static bool qcom_mdt_bins_are_split(const struct firmware *fw)
> +{
> +	const struct elf32_phdr *phdrs;
> +	const struct elf32_hdr *ehdr;
> +	uint64_t seg_start, seg_end;
> +	int i;
> +
> +	ehdr = (struct elf32_hdr *)fw->data;
> +	phdrs = (struct elf32_phdr *)(ehdr + 1);
> +
> +	for (i = 0; i < ehdr->e_phnum; i++) {
> +		seg_start = phdrs[i].p_offset;
> +		seg_end = phdrs[i].p_offset + phdrs[i].p_filesz;
> +		if (seg_start > fw->size || seg_end > fw->size)
> +			return true;
> +	}
> +
> +	return false;
> +}
> +
>  static ssize_t mdt_load_split_segment(void *ptr, const struct elf32_phdr *phdrs,
>  				      unsigned int segment, const char *fw_name,
>  				      struct device *dev)
> @@ -167,23 +187,13 @@ void *qcom_mdt_read_metadata(const struct firmware *fw, size_t *data_len,
>  	/* Copy ELF header */
>  	memcpy(data, fw->data, ehdr_size);
>  

The existing code handles 3 cases:

> -	if (ehdr_size + hash_size == fw->size) {

1) File is split, but hash resides with the ELF header in the .mdt

> -		/* Firmware is split and hash is packed following the ELF header */
> -		hash_offset = phdrs[0].p_filesz;
> -		memcpy(data + ehdr_size, fw->data + hash_offset, hash_size);
> -	} else if (phdrs[hash_segment].p_offset + hash_size <= fw->size) {

2) The hash segment exists in a segment of its own, but in the loaded
   image.

> -		/* Hash is in its own segment, but within the loaded file */
> +
> +	if (qcom_mdt_bins_are_split(fw)) {
> +		ret = mdt_load_split_segment(data + ehdr_size, phdrs, hash_segment, fw_name, dev);
> +	} else {
>  		hash_offset = phdrs[hash_segment].p_offset;
>  		memcpy(data + ehdr_size, fw->data + hash_offset, hash_size);
> -	} else {

3) The image is split, and the hash segment resides in it's own file.


Afaict the updated logic maintains #2 and #3, but drops #1. Please
review the git history to see if you can determine which target this
case exists with - and ask for someone to specifically verify your
change there.

Perhaps all your change is doing is removing case #1, in which case this
should be clear in the commit message; and we need to validate that your
new assumptions holds.

> -		/* Hash is in its own segment, beyond the loaded file */
> -		ret = mdt_load_split_segment(data + ehdr_size, phdrs, hash_segment, fw_name, dev);

For some reason you reversed the condition and got this out of the else
(seems like an unnecessary change)...but in the process you lost the
error handling below.

> -		if (ret) {
> -			kfree(data);
> -			return ERR_PTR(ret);
> -		}
>  	}
> -
>  	*data_len = ehdr_size + hash_size;
>  
>  	return data;
> @@ -270,6 +280,7 @@ static int __qcom_mdt_load(struct device *dev, const struct firmware *fw,
>  	phys_addr_t min_addr = PHYS_ADDR_MAX;
>  	ssize_t offset;
>  	bool relocate = false;
> +	bool is_split;
>  	void *ptr;
>  	int ret = 0;
>  	int i;
> @@ -277,6 +288,7 @@ static int __qcom_mdt_load(struct device *dev, const struct firmware *fw,
>  	if (!fw || !mem_region || !mem_phys || !mem_size)
>  		return -EINVAL;
>  
> +	is_split = qcom_mdt_bins_are_split(fw);
>  	ehdr = (struct elf32_hdr *)fw->data;
>  	phdrs = (struct elf32_phdr *)(ehdr + 1);
>  
> @@ -330,22 +342,16 @@ static int __qcom_mdt_load(struct device *dev, const struct firmware *fw,
>  
>  		ptr = mem_region + offset;
>  
> -		if (phdr->p_filesz && phdr->p_offset < fw->size &&
> -		    phdr->p_offset + phdr->p_filesz <= fw->size) {
> -			/* Firmware is large enough to be non-split */
> -			if (phdr->p_offset + phdr->p_filesz > fw->size) {
> -				dev_err(dev, "file %s segment %d would be truncated\n",
> -					fw_name, i);
> -				ret = -EINVAL;
> -				break;
> +		if (phdr->p_filesz) {

If you just change the condition (phr->p_filesz && !issplit), then your
patch becomes easier to read.

Regards,
Bjorn

> +			if (!is_split) {
> +				/* Firmware is large enough to be non-split */
> +				memcpy(ptr, fw->data + phdr->p_offset, phdr->p_filesz);
> +			} else {
> +				/* Firmware not large enough, load split-out segments */
> +				ret = mdt_load_split_segment(ptr, phdrs, i, fw_name, dev);
> +				if (ret)
> +					break;
>  			}
> -
> -			memcpy(ptr, fw->data + phdr->p_offset, phdr->p_filesz);
> -		} else if (phdr->p_filesz) {
> -			/* Firmware not large enough, load split-out segments */
> -			ret = mdt_load_split_segment(ptr, phdrs, i, fw_name, dev);
> -			if (ret)
> -				break;
>  		}
>  
>  		if (phdr->p_memsz > phdr->p_filesz)
> -- 
> 2.25.1
>