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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen stable-4.18] x86/ucode: Relax digest check when Entrysign is fixed in firmware
commit f6b0a04a432d2f1ba9c4d5317e4a010b58c401db
Author: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri Feb 28 23:17:13 2025 +0000
Commit: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Oct 28 18:18:20 2025 +0000
x86/ucode: Relax digest check when Entrysign is fixed in firmware
When Entrysign has been mitigated in firwmare, it is believed to be safe to
rely on the CPU patchloader again. This avoids us needing to maintain the
digest table for all new microcode indefinitely.
Relax the digest check when firmware looks to be up to date, and leave
behind
a clear message when not.
When the Zen6 (also Fam1ah processors) model numbers are known, they'll want
excluding from the range.
This is best-effort only. If a malicious microcode has been loaded prior to
Xen running, then all bets are off.
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
Release-Acked-By: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
(cherry picked from commit ff8228ab46582855eae78dd4cb62bba0e7e1fcba)
---
xen/arch/x86/cpu/microcode/amd.c | 86 ++++++++++++++++++++++++++++++++++--
xen/arch/x86/cpu/microcode/core.c | 2 +
xen/arch/x86/cpu/microcode/private.h | 2 +
3 files changed, 87 insertions(+), 3 deletions(-)
diff --git a/xen/arch/x86/cpu/microcode/amd.c b/xen/arch/x86/cpu/microcode/amd.c
index 45a7d4cc03..62b32ccb0c 100644
--- a/xen/arch/x86/cpu/microcode/amd.c
+++ b/xen/arch/x86/cpu/microcode/amd.c
@@ -102,6 +102,7 @@ static const struct patch_digest {
} patch_digests[] = {
#include "amd-patch-digests.c"
};
+static bool __ro_after_init entrysign_mitigiated_in_firmware;
static int cf_check cmp_patch_id(const void *key, const void *elem)
{
@@ -123,11 +124,11 @@ static bool check_digest(const struct container_microcode
*mc)
/*
* Zen1 thru Zen5 CPUs are known to use a weak signature algorithm on
- * microcode updates. Mitigate by checking the digest of the patch
- * against a list of known provenance.
+ * microcode updates. If this has not been mitigated in firmware, check
+ * the digest of the patch against a list of known provenance.
*/
if ( boot_cpu_data.x86 < 0x17 || boot_cpu_data.x86 > 0x1a ||
- !opt_digest_check )
+ entrysign_mitigiated_in_firmware || !opt_digest_check )
return true;
pd = bsearch(&patch->patch_id, patch_digests, ARRAY_SIZE(patch_digests),
@@ -553,3 +554,82 @@ const struct microcode_ops __initconst_cf_clobber
amd_ucode_ops = {
.apply_microcode = apply_microcode,
.compare_patch = compare_patch,
};
+
+/*
+ * The Entrysign vulnerability affects all Zen1 thru Zen5 CPUs. Firmware
+ * fixes were produced from Nov 2024. Zen3 thru Zen5 can continue to take
+ * OS-loadable microcode updates using a new signature scheme, as long as
+ * firmware has been updated first.
+ */
+void __init amd_check_entrysign(void)
+{
+ unsigned int curr_rev;
+ uint8_t fixed_rev;
+
+ if ( boot_cpu_data.x86_vendor != X86_VENDOR_AMD ||
+ boot_cpu_data.x86 < 0x17 ||
+ boot_cpu_data.x86 > 0x1a )
+ return;
+
+ /*
+ * Table taken from Linux, which is the only known source of information
+ * about client revisions. Note, Linux expresses "last-vulnerable-rev"
+ * while Xen wants "first-fixed-rev".
+ */
+ curr_rev = this_cpu(cpu_sig).rev;
+ switch ( curr_rev >> 8 )
+ {
+ case 0x080012: fixed_rev = 0x78; break;
+ case 0x080082: fixed_rev = 0x10; break;
+ case 0x083010: fixed_rev = 0x7d; break;
+ case 0x086001: fixed_rev = 0x0f; break;
+ case 0x086081: fixed_rev = 0x09; break;
+ case 0x087010: fixed_rev = 0x35; break;
+ case 0x08a000: fixed_rev = 0x0b; break;
+ case 0x0a0010: fixed_rev = 0x7b; break;
+ case 0x0a0011: fixed_rev = 0xdb; break;
+ case 0x0a0012: fixed_rev = 0x44; break;
+ case 0x0a0082: fixed_rev = 0x0f; break;
+ case 0x0a1011: fixed_rev = 0x54; break;
+ case 0x0a1012: fixed_rev = 0x4f; break;
+ case 0x0a1081: fixed_rev = 0x0a; break;
+ case 0x0a2010: fixed_rev = 0x30; break;
+ case 0x0a2012: fixed_rev = 0x13; break;
+ case 0x0a4041: fixed_rev = 0x0a; break;
+ case 0x0a5000: fixed_rev = 0x14; break;
+ case 0x0a6012: fixed_rev = 0x0b; break;
+ case 0x0a7041: fixed_rev = 0x0a; break;
+ case 0x0a7052: fixed_rev = 0x09; break;
+ case 0x0a7080: fixed_rev = 0x0a; break;
+ case 0x0a70c0: fixed_rev = 0x0a; break;
+ case 0x0aa001: fixed_rev = 0x17; break;
+ case 0x0aa002: fixed_rev = 0x19; break;
+ case 0x0b0021: fixed_rev = 0x47; break;
+ case 0x0b1010: fixed_rev = 0x47; break;
+ case 0x0b2040: fixed_rev = 0x32; break;
+ case 0x0b4040: fixed_rev = 0x32; break;
+ case 0x0b6000: fixed_rev = 0x32; break;
+ case 0x0b7000: fixed_rev = 0x32; break;
+ default:
+ printk(XENLOG_WARNING
+ "Unrecognised CPU %02x-%02x-%02x ucode 0x%08x, assuming
vulnerable to Entrysign\n",
+ boot_cpu_data.x86, boot_cpu_data.x86_model,
+ boot_cpu_data.x86_mask, curr_rev);
+ return;
+ }
+
+ /*
+ * This check is best-effort. If the platform looks to be out of date, it
+ * probably is. If the platform looks to be fixed, it either genuinely
+ * is, or malware has gotten in before Xen booted and all bets are off.
+ */
+ if ( (uint8_t)curr_rev >= fixed_rev )
+ {
+ entrysign_mitigiated_in_firmware = true;
+ return;
+ }
+
+ printk(XENLOG_WARNING
+ "WARNING: Platform vulnerable to Entrysign (SB-7033,
CVE-2024-36347) - firmware update required\n");
+ add_taint(TAINT_CPU_OUT_OF_SPEC);
+}
diff --git a/xen/arch/x86/cpu/microcode/core.c
b/xen/arch/x86/cpu/microcode/core.c
index 22330099df..e882e3e011 100644
--- a/xen/arch/x86/cpu/microcode/core.c
+++ b/xen/arch/x86/cpu/microcode/core.c
@@ -922,6 +922,8 @@ int __init early_microcode_init(unsigned long *module_map,
return -ENODEV;
}
+ amd_check_entrysign();
+
microcode_grab_module(module_map, mbi, mods);
if ( ucode_mod.mod_end || ucode_blob.size )
diff --git a/xen/arch/x86/cpu/microcode/private.h
b/xen/arch/x86/cpu/microcode/private.h
index 158cbda9cc..c8730da5d8 100644
--- a/xen/arch/x86/cpu/microcode/private.h
+++ b/xen/arch/x86/cpu/microcode/private.h
@@ -69,6 +69,8 @@ extern bool opt_digest_check;
*/
bool intel_can_load_microcode(void);
+void amd_check_entrysign(void);
+
extern const struct microcode_ops amd_ucode_ops, intel_ucode_ops;
#endif /* ASM_X86_MICROCODE_PRIVATE_H */
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.18
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