[PATCH 09/12] x86/microcode/AMD: Track patch allocation size explicitly

Kees Cook
2022-09-22T03:10:29Z

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 fixes
potential future issues where runtime bounds checking will notice that
the buffer was allocated to a smaller value than returned by ksize().

Suggested-by: Daniel Micay <danielmicay@gmail.com>
Link: https://lore.kernel.org/lkml/CA+DvKQ+bp7Y7gmaVhacjv9uF6Ar-o4tet872h4Q8RPYPJjcJQA@mail.gmail.com/
Fixes: 757885e94a22 ("x86, microcode, amd: Early microcode patch loading support for AMD")
Cc: Borislav Petkov <bp@alien8.de>
Cc: x86@kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
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 0c3d3440fe27..aa675783412f 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 8b2fcdfa6d31..615bc6efa1dd 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;
}
--
2.34.1