[xen staging] x86/ucode/amd: Fix OoB read in cpu_request_microcode()

[patchbot@xxxxxxx]

commit 1cbc4d89c45cba3929f1c0cb4bca0b000c4f174b
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Feb 9 22:10:54 2021 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Wed Feb 10 13:23:51 2021 +0000

    x86/ucode/amd: Fix OoB read in cpu_request_microcode()
    
    verify_patch_size() is a maximum size check, and doesn't have a minimum 
bound.
    
    If the microcode container encodes a blob with a length less than 64 bytes,
    the subsequent calls to microcode_fits()/compare_header() may read off the 
end
    of the buffer.
    
    Fixes: 4de936a38a ("x86/ucode/amd: Rework parsing logic in 
cpu_request_microcode()")
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/cpu/microcode/amd.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/xen/arch/x86/cpu/microcode/amd.c b/xen/arch/x86/cpu/microcode/amd.c
index 5255028af7..3e51e53c1f 100644
--- a/xen/arch/x86/cpu/microcode/amd.c
+++ b/xen/arch/x86/cpu/microcode/amd.c
@@ -349,6 +349,7 @@ static struct microcode_patch *cpu_request_microcode(const 
void *buf, size_t siz
             if ( size < sizeof(*mc) ||
                  (mc = buf)->type != UCODE_UCODE_TYPE ||
                  size - sizeof(*mc) < mc->len ||
+                 mc->len < sizeof(struct microcode_patch) ||
                  (!skip_ucode && !verify_patch_size(mc->len)) )
             {
                 printk(XENLOG_ERR "microcode: Bad microcode data\n");
--
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