Re: [PATCH v5 3/6] x86/microcode/AMD: Check microcode container data in the early loader

Borislav Petkov
2018-04-30T09:05:41Z

On Mon, Apr 23, 2018 at 11:34:08PM +0200, Maciej S. Szmigiero wrote:
> This commit converts the early loader in the AMD microcode update driver to

Avoid beginning the commit message of a patch with "This patch" or "This
commit". It is tautologically useless. Simply get to the point directly:

"Convert the container parsing function ... "

> use the container data checking functions introduced by the previous
> commit.
>
> We have to be careful to call these functions with 'early' parameter set,
> so they won't try to print errors as the early loader runs too early for
> printk()-style functions to work.
>
> Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
> ---
> arch/x86/kernel/cpu/microcode/amd.c | 45 ++++++++++++++++++-------------------
> 1 file changed, 22 insertions(+), 23 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
> index 4fafaf0852d7..94fcd702a67a 100644
> --- a/arch/x86/kernel/cpu/microcode/amd.c
> +++ b/arch/x86/kernel/cpu/microcode/amd.c
> @@ -216,29 +216,33 @@ static bool verify_patch(u8 family, const u8 *buf, size_t buf_size, bool early)
> * Returns the amount of bytes consumed while scanning. @desc contains all the
> * data we're going to use in later stages of the application.
> */
> -static ssize_t parse_container(u8 *ucode, ssize_t size, struct cont_desc *desc)
> +static size_t parse_container(u8 *ucode, size_t size, struct cont_desc *desc)
> {
> struct equiv_cpu_entry *eq;
> - ssize_t orig_size = size;
> + size_t orig_size = size;
> u32 *hdr = (u32 *)ucode;
> + u32 equiv_tbl_len;
> u16 eq_id;
> u8 *buf;
>
> - /* Am I looking at an equivalence table header? */
> - if (hdr[0] != UCODE_MAGIC ||
> - hdr[1] != UCODE_EQUIV_CPU_TABLE_TYPE ||
> - hdr[2] == 0)
> + if (!verify_container(ucode, size, true))
> + return 0;

return CONTAINER_HDR_SZ;

We want to make some forward progress after all.

> + if (!verify_equivalence_table(ucode, size, true))
> return CONTAINER_HDR_SZ;
>
> buf = ucode;
>
> + equiv_tbl_len = hdr[2];
> eq = (struct equiv_cpu_entry *)(buf + CONTAINER_HDR_SZ);
>
> /* Find the equivalence ID of our CPU in this table: */
> eq_id = find_equiv_id(eq, desc->cpuid_1_eax);
>
> - buf += hdr[2] + CONTAINER_HDR_SZ;
> - size -= hdr[2] + CONTAINER_HDR_SZ;
> + buf += CONTAINER_HDR_SZ;
> + buf += equiv_tbl_len;
> + size -= CONTAINER_HDR_SZ;
> + size -= equiv_tbl_len;
>
> /*
> * Scan through the rest of the container to find where it ends. We do
> @@ -250,25 +254,22 @@ static ssize_t parse_container(u8 *ucode, ssize_t size, struct cont_desc *desc)
>
> hdr = (u32 *)buf;
>
> - if (hdr[0] != UCODE_UCODE_TYPE)
> + if (!verify_patch_section(buf, size, true))

So there's verify_patch_section(), verify_patch() and
verify_patch_size() now. One of the three looks redundant to me. Sounds
to me verify_patch_size() could be expanded into verify_patch() and
former dropped.

> break;
>
> - /* Sanity-check patch size. */
> patch_size = hdr[1];
> - if (patch_size > PATCH_MAX_SIZE)
> - break;
>
> - /* Skip patch section header: */
> - buf += SECTION_HDR_SIZE;
> - size -= SECTION_HDR_SIZE;
> -
> - mc = (struct microcode_amd *)buf;
> - if (eq_id == mc->hdr.processor_rev_id) {
> + mc = (struct microcode_amd *)(buf + SECTION_HDR_SIZE);
> + if (eq_id == mc->hdr.processor_rev_id &&
> + verify_patch(x86_family(desc->cpuid_1_eax), buf, size,
> + true)) {

This needs to be made readable.

--
Regards/Gruss,
Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.