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[PATCH v2] SUPPORT.md: Un-shimmed 32-bit PV guests are no longer supported

  • To: <security@xxxxxxxxxxxxxx>
  • From: George Dunlap <george.dunlap@xxxxxxxxxx>
  • Date: Thu, 6 May 2021 13:47:52 +0100
  • Authentication-results: esa5.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none
  • Cc: <xen-devel@xxxxxxxxxxxxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Jann Horn <jannh@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>
  • Delivery-date: Thu, 06 May 2021 12:48:10 +0000
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The support status of 32-bit guests doesn't seem particularly useful.

With it changed to fully unsupported outside of PV-shim, adjust the PV32
Kconfig default accordingly.

Reported-by: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
 - add in Kconfig from advisory, ported over c/s d23d792478d
 SUPPORT.md           | 9 +--------
 xen/arch/x86/Kconfig | 7 +++++--
 2 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/SUPPORT.md b/SUPPORT.md
index d0d4fc6f4f..a29680e04c 100644
--- a/SUPPORT.md
+++ b/SUPPORT.md
@@ -86,14 +86,7 @@ No hardware requirements
     Status, x86_64: Supported
     Status, x86_32, shim: Supported
-    Status, x86_32, without shim: Supported, with caveats
-Due to architectural limitations,
-32-bit PV guests must be assumed to be able to read arbitrary host memory
-using speculative execution attacks.
-Advisories will continue to be issued
-for new vulnerabilities related to un-shimmed 32-bit PV guests
-enabling denial-of-service attacks or privilege escalation attacks.
+    Status, x86_32, without shim: Supported, not security supported
 ### x86/HVM
diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
index e55e029b79..9b164db641 100644
--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -55,7 +55,7 @@ config PV
 config PV32
        bool "Support for 32bit PV guests"
        depends on PV
-       default y
+       default PV_SHIM
        select COMPAT
          The 32bit PV ABI uses Ring1, an area of the x86 architecture which
@@ -67,7 +67,10 @@ config PV32
          reduction, or performance reasons.  Backwards compatibility can be
          provided via the PV Shim mechanism.
-         If unsure, say Y.
+         Note that outside of PV Shim, 32-bit PV guests are not security
+         supported anymore.
+         If unsure, use the default setting.
 config PV_LINEAR_PT
        bool "Support for PV linear pagetables"



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