On Tue, Apr 18, 2023 at 09:44:09AM -0400, Stefan Berger wrote:
> The memory area of the TPM measurement log is currently not properly
> duplicated for carrying it across kexec when an Open Firmware
> Devicetree is used. Therefore, the contents of the log get corrupted.
> Fix this for the kexec_file_load() syscall by allocating a buffer and
> copying the contents of the existing log into it. The new buffer is
> preserved across the kexec and a pointer to it is available when the new
> kernel is started. To achieve this, store the allocated buffer's address
> in the flattened device tree (fdt) under the name linux,tpm-kexec-buffer
> and search for this entry early in the kernel startup before the TPM
> subsystem starts up. Adjust the pointer in the of-tree stored under
> linux,sml-base to point to this buffer holding the preserved log. The TPM
> driver can then read the base address from this entry when making the log
> available. Invalidate the log by removing 'linux,sml-base' from the
> devicetree if anything goes wrong with updating the buffer.
>
> Use subsys_initcall() to call the function to restore the buffer even if
> the TPM subsystem or driver are not used. This allows the buffer to be
> carried across the next kexec without involvement of the TPM subsystem
> and ensures a valid buffer pointed to by the of-tree.
Hi Stefan,
some minor feedback from my side.
> Use the subsys_initcall(), rather than an ealier initcall, since
nit via checkpatch.pl --codespell: s/ealier/earlier/
> page_is_ram() in get_kexec_buffer() only starts working at this stage.
>
> Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
> Cc: Rob Herring <robh+dt@xxxxxxxxxx>
> Cc: Frank Rowand <frowand.list@xxxxxxxxx>
> Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
> Tested-by: Nageswara R Sastry <rnsastry@xxxxxxxxxxxxx>
> Tested-by: Coiby Xu <coxu@xxxxxxxxxx>
> Reviewed-by: Rob Herring <robh@xxxxxxxxxx>
...
> +void tpm_add_kexec_buffer(struct kimage *image)
> +{
> + struct kexec_buf kbuf = { .image = image, .buf_align = 1,
> + .buf_min = 0, .buf_max = ULONG_MAX,
> + .top_down = true };
> + struct device_node *np;
> + void *buffer;
> + u32 size;
> + u64 base;
> + int ret;
> +
> + if (!IS_ENABLED(CONFIG_PPC64))
> + return;
> +
> + np = of_find_node_by_name(NULL, "vtpm");
> + if (!np)
> + return;
> +
> + if (of_tpm_get_sml_parameters(np, &base, &size) < 0)
> + return;
> +
> + buffer = vmalloc(size);
> + if (!buffer)
> + return;
> + memcpy(buffer, __va(base), size);
> +
> + kbuf.buffer = buffer;
> + kbuf.bufsz = size;
> + kbuf.memsz = size;
> + ret = kexec_add_buffer(&kbuf);
> + if (ret) {
> + pr_err("Error passing over kexec TPM measurement log buffer: %d\n",
> + ret);
Does buffer need to be freed here?
> + return;
> + }
> +
> + image->tpm_buffer = buffer;
> + image->tpm_buffer_addr = kbuf.mem;
> + image->tpm_buffer_size = size;
> +}
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