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SubjectRe: [PATCH v3 2/9] x86/microcode/AMD: check whether the equivalence table fits in the file
On Tue, Mar 13, 2018 at 10:06:23PM +0100, Maciej S. Szmigiero wrote:
> Before loading a CPU equivalence table from a microcode container file we
> need to verify whether this file is actually large enough to contain the
> table of a size indicated in this file.
> If it is not, there is no point of continuing with loading it since
> microcode patches are located after the equivalence table anyway.
>
> Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
> ---
> arch/x86/kernel/cpu/microcode/amd.c | 54 ++++++++++++++++++++++++++-----------
> 1 file changed, 38 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
> index ffe0d0ce57fc..ac06e2819f26 100644
> --- a/arch/x86/kernel/cpu/microcode/amd.c
> +++ b/arch/x86/kernel/cpu/microcode/amd.c
> @@ -80,20 +80,29 @@ static u16 find_equiv_id(struct equiv_cpu_entry *equiv_table, u32 sig)
> * 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;
> + size_t eq_size;
> u16 eq_id;
> u8 *buf;
>
> /* Am I looking at an equivalence table header? */

That comment becomes wrong when you add this check here.

> + if (size < CONTAINER_HDR_SZ)
> + return 0;
> +
> if (hdr[0] != UCODE_MAGIC ||
> hdr[1] != UCODE_EQUIV_CPU_TABLE_TYPE ||
> hdr[2] == 0)
> return CONTAINER_HDR_SZ;
>
> + eq_size = hdr[2];

If we're going to have special local vars for the container header, then
do it right:

cont_magic = hdr[0];
cont_type = hdr[1];
equiv_tbl_len = hdr[2];

and then use those from now on.

> + if (eq_size < sizeof(*eq) ||
> + size - CONTAINER_HDR_SZ < eq_size)
> + return 0;

I think you want

if (size < eqiv_tbl_len + CONTAINER_HDR_SZ)
return size;

here to skip over the next, hopefully not truncated container.

> +
> buf = ucode;
>
> eq = (struct equiv_cpu_entry *)(buf + CONTAINER_HDR_SZ);
> @@ -101,8 +110,8 @@ static ssize_t parse_container(u8 *ucode, ssize_t size, struct cont_desc *desc)
> /* 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 += eq_size + CONTAINER_HDR_SZ;
> + size -= eq_size + CONTAINER_HDR_SZ;
>
> /*
> * Scan through the rest of the container to find where it ends. We do
> @@ -159,15 +168,13 @@ static ssize_t parse_container(u8 *ucode, ssize_t size, struct cont_desc *desc)
> */
> static void scan_containers(u8 *ucode, size_t size, struct cont_desc *desc)
> {
> - ssize_t rem = size;
> -
> - while (rem >= 0) {
> - ssize_t s = parse_container(ucode, rem, desc);
> + while (size > 0) {
> + size_t s = parse_container(ucode, size, desc);
> if (!s)
> return;
>
> ucode += s;
> - rem -= s;
> + size -= s;
> }
> }
>

All changes upto here need to be a separate patch.
install_equiv_cpu_table() changes below are the second patch.

> @@ -540,15 +547,30 @@ static enum ucode_state apply_microcode_amd(int cpu)
> return UCODE_UPDATED;
> }
>
> -static int install_equiv_cpu_table(const u8 *buf)
> +static int install_equiv_cpu_table(const u8 *buf, size_t buf_size)
> {
> unsigned int *ibuf = (unsigned int *)buf;
> - unsigned int type = ibuf[1];
> - unsigned int size = ibuf[2];
> + unsigned int type, size;

unsigned int type, equiv_tbl_len;

> +
> + if (buf_size < CONTAINER_HDR_SZ) {

<= is ok too.

> + pr_err("no container header\n");

More descriptive error messages:

"Truncated microcode container header.\n"

> + return -EINVAL;
> + }
> +
> + type = ibuf[1];
> + if (type != UCODE_EQUIV_CPU_TABLE_TYPE) {
> + pr_err("invalid type field in container file section header\n");

"Wrong microcode container equivalence table type: %d.\n"

> + return -EINVAL;
> + }
> +
> + size = ibuf[2];
> + if (size < sizeof(struct equiv_cpu_entry)) {
> + pr_err("equivalent CPU table too short\n");

"Truncated equivalence table.\n"

> + return -EINVAL;
> + }
>
> - if (type != UCODE_EQUIV_CPU_TABLE_TYPE || !size) {
> - pr_err("empty section/"
> - "invalid type field in container file section header\n");
> + if (buf_size - CONTAINER_HDR_SZ < size) {
> + pr_err("equivalent CPU table truncated\n");

Combine that test with the above one and use the same error message.

Thx.

--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.

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