xen: patch with XSA-515

Xen Security Advisory CVE-2026-79608 / XSA-515

               x86/AMD: ineffectual Zenbleed workaround

The workaround for XSA-433 (Zenbleed, CVE-2023-20593) was later
re-worked to better integrate with other manipulations of the same MSR.
In this rework an inverted conditional was introduced, resulting in the
workaround to not be applied when needed and vice versa.

For more details, see:
  http://xenbits.xen.org/xsa/advisory-433.html

An attacker can exploit this bug to read data from different contexts on
the same core.  Examples of such data includes key material, cypher and
plaintext from the AES-NI instructions, or the contents of REP-MOVS
instructions, commonly used to implement memcpy().

https://xenbits.xenproject.org/xsa/advisory-515.html

Signed-off-by: Fernando Rodrigues <alpha@sigmasquadron.net>

(cherry picked from commit 25bdf0cbd4)

Signed-off-by: Fernando Rodrigues <alpha@sigmasquadron.net>

pkgs/by-name/xe/xen/package.nix

@@ -209,6 +209,11 @@ stdenv.mkDerivation (finalAttrs: {
       url = "https://xenbits.xenproject.org/xsa/xsa512-2.patch";
       hash = "sha256-4LgqC1F22kFjiVWgiSb1hZazbBF2Fziiif0Scv+ynho=";
     })
+
+    (fetchpatch {
+      url = "https://xenbits.xenproject.org/xsa/xsa515.patch";
+      hash = "sha256-p4/eNfnR/KL1QZ+6Ml4eWyMibXr1DEcBzhQ6XrKVVhM=";
+    })
   ]
   ++ optionals (versionOlder finalAttrs.version "4.21") [
     # Patch `libxl` to search for `qemu-system-i386` properly.