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Subject[PATCH 06/16] x86/microcode/AMD: Concentrate patch verification
Date
From: Borislav Petkov <bp@suse.de>

Add a verify_patch() function which tries to sanity-check many aspects
of a microcode patch supplied by an outside container before attempting
a load.

Prepend all sub-functions' names which verify an aspect of a microcode
patch with "__".

Call it in verify_and_add_patch() *before* looking at the microcode
header.

Signed-off-by: Borislav Petkov <bp@suse.de>
---
arch/x86/kernel/cpu/microcode/amd.c | 79 ++++++++++++++++++++---------
1 file changed, 54 insertions(+), 25 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index a94a15aacfe7..8f012a7f88c4 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -139,11 +139,15 @@ static bool verify_equivalence_table(const u8 *buf, size_t buf_size, bool early)
* Check whether there is a valid, non-truncated microcode patch section at the
* beginning of @buf of size @buf_size. Set @early to use this function in the
* early path.
+ *
+ * On success, @sh_psize returns the patch size according to the section header,
+ * to the caller.
*/
-static bool verify_patch_section(const u8 *buf, size_t buf_size, bool early)
+static bool
+__verify_patch_section(const u8 *buf, size_t buf_size, u32 *sh_psize, bool early)
{
+ u32 p_type, p_size;
const u32 *hdr;
- u32 patch_type, patch_size;

if (buf_size < SECTION_HDR_SIZE) {
if (!early)
@@ -153,24 +157,26 @@ static bool verify_patch_section(const u8 *buf, size_t buf_size, bool early)
}

hdr = (const u32 *)buf;
- patch_type = hdr[0];
- patch_size = hdr[1];
+ p_type = hdr[0];
+ p_size = hdr[1];

- if (patch_type != UCODE_UCODE_TYPE) {
+ if (p_type != UCODE_UCODE_TYPE) {
if (!early)
pr_debug("Invalid type field (0x%x) in container file section header.\n",
- patch_type);
+ p_type);

return false;
}

- if (patch_size < sizeof(struct microcode_header_amd)) {
+ if (p_size < sizeof(struct microcode_header_amd)) {
if (!early)
- pr_debug("Patch of size %u too short.\n", patch_size);
+ pr_debug("Patch of size %u too short.\n", p_size);

return false;
}

+ *sh_psize = p_size;
+
return true;
}

@@ -181,7 +187,7 @@ static bool verify_patch_section(const u8 *buf, size_t buf_size, bool early)
* header.
*/
static unsigned int
-verify_patch_size(u8 family, u32 sh_psize, unsigned int buf_size)
+__verify_patch_size(u8 family, u32 sh_psize, unsigned int buf_size)
{
u32 max_size;

@@ -212,6 +218,34 @@ verify_patch_size(u8 family, u32 sh_psize, unsigned int buf_size)
return sh_psize;
}

+static unsigned int
+verify_patch(u8 family, const u8 *buf, unsigned int buf_size, bool early)
+{
+ u32 sh_psize;
+
+ if (!__verify_patch_section(buf, buf_size, &sh_psize, early))
+ return 0;
+ /*
+ * 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.
+ */
+ buf_size -= SECTION_HDR_SIZE;
+
+ /*
+ * Check if the remaining buffer is big enough to contain a patch of
+ * size sh_psize, as the section claims.
+ */
+ if (buf_size < sh_psize) {
+ if (!early)
+ pr_debug("Patch of size %u truncated.\n", sh_psize);
+
+ return 0;
+ }
+
+ return __verify_patch_size(family, sh_psize, buf_size);
+}
+
/*
* This scans the ucode blob for the proper container as we can have multiple
* containers glued together. Returns the equivalence ID from the equivalence
@@ -687,7 +721,7 @@ static void cleanup(void)
}

/*
- * We return the current size even if some of the checks failed so that
+ * Return a non-negative value even if some of the checks failed so that
* we can skip over the next patch. If we return a negative value, we
* signal a grave error like a memory allocation has failed and the
* driver cannot continue functioning normally. In such cases, we tear
@@ -695,14 +729,20 @@ static void cleanup(void)
*/
static int verify_and_add_patch(u8 family, u8 *fw, unsigned int leftover)
{
- unsigned int sh_psize, crnt_size, ret;
struct microcode_header_amd *mc_hdr;
+ unsigned int patch_size, crnt_size;
struct ucode_patch *patch;
u32 proc_fam;
u16 proc_id;

- sh_psize = *(u32 *)(fw + 4);
- crnt_size = sh_psize + SECTION_HDR_SIZE;
+ patch_size = verify_patch(family, fw, leftover, false);
+ if (!patch_size) {
+ pr_debug("Patch size mismatch.\n");
+ return 1;
+ }
+
+ /* If initial rough pokes pass, we can start looking at the header. */
+ crnt_size = patch_size + SECTION_HDR_SIZE;
mc_hdr = (struct microcode_header_amd *)(fw + SECTION_HDR_SIZE);
proc_id = mc_hdr->processor_rev_id;

@@ -723,24 +763,13 @@ static int verify_and_add_patch(u8 family, u8 *fw, unsigned int leftover)
return crnt_size;
}

- /*
- * 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.
- */
- ret = verify_patch_size(family, sh_psize, leftover - SECTION_HDR_SIZE);
- if (!ret) {
- pr_err("Patch-ID 0x%08x: size mismatch.\n", mc_hdr->patch_id);
- return crnt_size;
- }
-
patch = kzalloc(sizeof(*patch), GFP_KERNEL);
if (!patch) {
pr_err("Patch allocation failure.\n");
return -EINVAL;
}

- patch->data = kmemdup(fw + SECTION_HDR_SIZE, sh_psize, GFP_KERNEL);
+ patch->data = kmemdup(fw + SECTION_HDR_SIZE, patch_size, GFP_KERNEL);
if (!patch->data) {
pr_err("Patch data allocation failure.\n");
kfree(patch);
--
2.19.1
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