[Xen-devel] [PATCH] x86/ucode/amd: Fix buffer overrun with equiv table handling

[Xen-devel] [PATCH] x86/ucode/amd: Fix buffer overrun with equiv table handling

[Andrew Cooper]

find_equiv_cpu_id() loops until it finds a 0 installed_cpu entry.  Well formed
AMD microcode containers have this property.

Extend the checking in install_equiv_cpu_table() to reject tables which don't
have a sentinal at the end.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>

All of this logic needs rewriting, but this is the minimally invasive version
for backport.
---
 xen/arch/x86/cpu/microcode/amd.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/cpu/microcode/amd.c b/xen/arch/x86/cpu/microcode/amd.c
index b8b83d248d..9fe1a3c941 100644
--- a/xen/arch/x86/cpu/microcode/amd.c
+++ b/xen/arch/x86/cpu/microcode/amd.c
@@ -310,6 +310,7 @@ static int install_equiv_cpu_table(
     size_t *offset)
 {
     const struct mpbhdr *mpbuf = data + *offset + 4;
+    const struct equiv_cpu_entry *eq;
 
     *offset += mpbuf->len + CONT_HDR_SIZE;	/* add header length */
 
@@ -319,7 +320,9 @@ static int install_equiv_cpu_table(
         return -EINVAL;
     }
 
-    if ( mpbuf->len == 0 )
+    if ( mpbuf->len == 0 || mpbuf->len % sizeof(*eq) ||
+         (eq = (const void *)mpbuf->data,
+          eq[(mpbuf->len / sizeof(*eq)) - 1].installed_cpu) )
     {
         printk(KERN_ERR "microcode: Wrong microcode equivalent cpu table length\n");
         return -EINVAL;
-- 
2.11.0

Re: [Xen-devel] [PATCH] x86/ucode/amd: Fix buffer overrun with equiv table handling

[Jan Beulich]

On 27.03.2020 12:59, Andrew Cooper wrote:
> find_equiv_cpu_id() loops until it finds a 0 installed_cpu entry.  Well formed
> AMD microcode containers have this property.

With this, would you mind adding "potential" to the subject?

> Extend the checking in install_equiv_cpu_table() to reject tables which don't
> have a sentinal at the end.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>