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    Subject[PATCH v7 2/9] x86/microcode/AMD: Add microcode container data checking functions
    Date
    Add verify_container(), verify_equivalence_table(), verify_patch_section()
    and verify_patch() functions to the AMD microcode update driver.

    These functions check whether a passed buffer contains the relevant
    structure, whether it isn't truncated and (for actual microcode patches)
    whether the size of a patch is not too large for a particular CPU family.
    By adding these checks as separate functions the actual microcode loading
    code won't get interspersed with a lot of checks and so will be more
    readable.

    Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
    ---
    arch/x86/kernel/cpu/microcode/amd.c | 180 +++++++++++++++++++++++++++-
    1 file changed, 177 insertions(+), 3 deletions(-)

    diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
    index dc8ea9a9d962..120778771909 100644
    --- a/arch/x86/kernel/cpu/microcode/amd.c
    +++ b/arch/x86/kernel/cpu/microcode/amd.c
    @@ -73,6 +73,182 @@ static u16 find_equiv_id(struct equiv_cpu_entry *equiv_table, u32 sig)
    return 0;
    }

    +/*
    + * Check whether there is a valid microcode container file at the beginning
    + * of a passed buffer @buf of size @buf_size.
    + * If @early is set do not print errors so this function is usable by the
    + * early microcode loader.
    + */
    +static bool verify_container(const u8 *buf, size_t buf_size, bool early)
    +{
    + u32 cont_magic;
    +
    + if (buf_size <= CONTAINER_HDR_SZ) {
    + if (!early)
    + pr_err("Truncated microcode container header.\n");
    +
    + return false;
    + }
    +
    + cont_magic = *(const u32 *)buf;
    + if (cont_magic != UCODE_MAGIC) {
    + if (!early)
    + pr_err("Invalid magic value (0x%08x).\n", cont_magic);
    +
    + return false;
    + }
    +
    + return true;
    +}
    +
    +/*
    + * Check whether there is a valid, non-truncated CPU equivalence table
    + * at the beginning of a passed buffer @buf of size @buf_size.
    + * If @early is set do not print errors so this function is usable by the
    + * early microcode loader.
    + */
    +static bool verify_equivalence_table(const u8 *buf, size_t buf_size, bool early)
    +{
    + const u32 *hdr = (const u32 *)buf;
    + u32 cont_type, equiv_tbl_len;
    +
    + if (!verify_container(buf, buf_size, early))
    + return false;
    +
    + cont_type = hdr[1];
    + if (cont_type != UCODE_EQUIV_CPU_TABLE_TYPE) {
    + if (!early)
    + pr_err("Wrong microcode container equivalence table type: %u.\n",
    + cont_type);
    +
    + return false;
    + }
    +
    + equiv_tbl_len = hdr[2];
    + if (equiv_tbl_len < sizeof(struct equiv_cpu_entry) ||
    + buf_size - CONTAINER_HDR_SZ < equiv_tbl_len) {
    + if (!early)
    + pr_err("Truncated equivalence table.\n");
    +
    + return false;
    + }
    +
    + return true;
    +}
    +
    +/*
    + * Check whether there is a valid, non-truncated microcode patch section
    + * at the beginning of a passed buffer @buf of size @buf_size.
    + * If @early is set do not print errors so this function is usable by the
    + * early microcode loader.
    + */
    +static bool verify_patch_section(const u8 *buf, size_t buf_size, bool early)
    +{
    + const u32 *hdr;
    + u32 patch_type, patch_size;
    +
    + if (buf_size < SECTION_HDR_SIZE) {
    + if (!early)
    + pr_err("Truncated patch section.\n");
    +
    + return false;
    + }
    +
    + hdr = (const u32 *)buf;
    + patch_type = hdr[0];
    + patch_size = hdr[1];
    +
    + if (patch_type != UCODE_UCODE_TYPE) {
    + if (!early)
    + pr_err("Invalid type field (%u) in container file section header.\n",
    + patch_type);
    +
    + return false;
    + }
    +
    + if (patch_size < sizeof(struct microcode_header_amd)) {
    + if (!early)
    + pr_err("Patch of size %u too short.\n", patch_size);
    +
    + return false;
    + }
    +
    + return true;
    +}
    +
    +static unsigned int verify_patch_size(u8 family, u32 patch_size,
    + unsigned int size);
    +
    +/*
    + * Check whether there is a valid, non-truncated microcode patch of the
    + * right size for a particular family @family at the beginning of a passed
    + * buffer @buf, buffer that is of size @buf_size.
    + * Will return the length of current patch data in @crnt_size (even on
    + * failure), so the caller knows how many bytes it should skip.
    + * If @early is set do not print errors so this function is usable by the
    + * early microcode loader.
    + */
    +static bool verify_patch(u8 family, const u8 *buf, size_t buf_size,
    + unsigned int *crnt_size, bool early)
    +{
    + const u32 *hdr;
    + u32 patch_size;
    + const struct microcode_header_amd *mc_hdr;
    + u8 patch_fam;
    +
    + if (!verify_patch_section(buf, buf_size, early)) {
    + *crnt_size = min_t(unsigned int, 1, buf_size);
    + return false;
    + }
    +
    + hdr = (const u32 *)buf;
    + patch_size = hdr[1];
    +
    + if (buf_size - SECTION_HDR_SIZE < patch_size) {
    + if (!early)
    + pr_err("Patch of size %u truncated.\n", patch_size);
    +
    + *crnt_size = buf_size;
    + return false;
    + }
    +
    + /*
    + * Set a patch length limit of slightly less than U32_MAX to
    + * prevent overflowing 32-bit variables holding the whole
    + * patch section size.
    + */
    + if (patch_size > U32_MAX - SECTION_HDR_SIZE) {
    + if (!early)
    + pr_err("Patch of size %u too large.\n", patch_size);
    +
    + *crnt_size = SECTION_HDR_SIZE + PATCH_MAX_SIZE;
    + return false;
    + }
    +
    + *crnt_size = SECTION_HDR_SIZE + patch_size;
    +
    + mc_hdr = (const struct microcode_header_amd *)(buf + SECTION_HDR_SIZE);
    + patch_fam = 0xf + (mc_hdr->processor_rev_id >> 12);
    +
    + /* Is the patch for the proper CPU family? */
    + if (family != patch_fam)
    + return false;
    +
    + /*
    + * The section header length is not included in this indicated size
    + * but is present in the leftover file length so we need to subtract
    + * it before passing this value to the function below.
    + */
    + if (!verify_patch_size(family, patch_size, buf_size - SECTION_HDR_SIZE)) {
    + if (!early)
    + pr_err("Patch of size %u too large.\n", patch_size);
    +
    + return false;
    + }
    +
    + return true;
    +}
    +
    /*
    * This scans the ucode blob for the proper container as we can have multiple
    * containers glued together. Returns the equivalence ID from the equivalence
    @@ -494,10 +670,8 @@ static unsigned int verify_patch_size(u8 family, u32 patch_size, unsigned int si
    break;
    }

    - if (patch_size > min_t(u32, size, max_size)) {
    - pr_err("patch size mismatch\n");
    + if (patch_size > min_t(u32, size, max_size))
    return 0;
    - }

    return patch_size;
    }
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