[tip: x86/microcode] x86/microcode/AMD: Track patch allocation size explicitly

[tip-bot2 for Kees Cook]

The following commit has been merged into the x86/microcode branch of tip:

Commit-ID:     712f210a457d9c32414df246a72781550bc23ef6
Gitweb:        https://git.kernel.org/tip/712f210a457d9c32414df246a72781550bc23ef6
Author:        Kees Cook <keescook@xxxxxxxxxxxx>
AuthorDate:    Wed, 21 Sep 2022 20:10:10 -07:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Fri, 23 Sep 2022 13:46:26 +02:00

x86/microcode/AMD: Track patch allocation size explicitly

In preparation for reducing the use of ksize(), record the actual
allocation size for later memcpy(). This avoids copying extra
(uninitialized!) bytes into the patch buffer when the requested
allocation size isn't exactly the size of a kmalloc bucket.
Additionally, fix potential future issues where runtime bounds checking
will notice that the buffer was allocated to a smaller value than
returned by ksize().

Fixes: 757885e94a22 ("x86, microcode, amd: Early microcode patch loading support for AMD")
Suggested-by: Daniel Micay <danielmicay@xxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lore.kernel.org/lkml/CA+DvKQ+bp7Y7gmaVhacjv9uF6Ar-o4tet872h4Q8RPYPJjcJQA@xxxxxxxxxxxxxx/
---
 arch/x86/include/asm/microcode.h    | 1 +
 arch/x86/kernel/cpu/microcode/amd.c | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/microcode.h b/arch/x86/include/asm/microcode.h
index 7f7800e..74ecc2b 100644
--- a/arch/x86/include/asm/microcode.h
+++ b/arch/x86/include/asm/microcode.h
@@ -9,6 +9,7 @@
 struct ucode_patch {
 	struct list_head plist;
 	void *data;		/* Intel uses only this one */
+	unsigned int size;
 	u32 patch_id;
 	u16 equiv_cpu;
 };
diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index 5f38dd7..e7410e9 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -788,6 +788,7 @@ static int verify_and_add_patch(u8 family, u8 *fw, unsigned int leftover,
 		kfree(patch);
 		return -EINVAL;
 	}
+	patch->size = *patch_size;
 
 	mc_hdr      = (struct microcode_header_amd *)(fw + SECTION_HDR_SIZE);
 	proc_id     = mc_hdr->processor_rev_id;
@@ -869,7 +870,7 @@ load_microcode_amd(bool save, u8 family, const u8 *data, size_t size)
 		return ret;
 
 	memset(amd_ucode_patch, 0, PATCH_MAX_SIZE);
-	memcpy(amd_ucode_patch, p->data, min_t(u32, ksize(p->data), PATCH_MAX_SIZE));
+	memcpy(amd_ucode_patch, p->data, min_t(u32, p->size, PATCH_MAX_SIZE));
 
 	return ret;
 }