[xen staging] SUPPORT.md: limit support statement for Linux and Windows frontends

[patchbot@xxxxxxx]

commit 22891e12a45f9bb2e1dbb5daf2ba39cbe002e4f4
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Tue Jan 11 11:43:48 2022 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jan 11 11:43:48 2022 +0100

    SUPPORT.md: limit support statement for Linux and Windows frontends
    
    Change the support state of Linux and Windows pv frontends from
    "supported" to "supported with caveats" in order to reflect that the
    frontends can probably be harmed by their respective backends.
    
    Some of the Linux frontends have been hardened already.
    
    This is XSA-376
    
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 SUPPORT.md | 57 ++++++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 48 insertions(+), 9 deletions(-)

diff --git a/SUPPORT.md b/SUPPORT.md
index 3a1fd1ba39..32fb0aa8de 100644
--- a/SUPPORT.md
+++ b/SUPPORT.md
@@ -417,7 +417,11 @@ Guest-side driver capable of speaking the Xen PV block 
protocol
     Status, FreeBSD: Supported, Security support external
     Status, NetBSD: Supported, Security support external
     Status, OpenBSD: Supported, Security support external
-    Status, Windows: Supported
+    Status, Windows: Supported, with caveats
+
+Windows frontend currently trusts the backend;
+bugs in the frontend which allow backend to cause mischief will not be
+considered security vulnerabilities.
 
 ### Netfront
 
@@ -427,20 +431,32 @@ Guest-side driver capable of speaking the Xen PV 
networking protocol
     Status, FreeBSD: Supported, Security support external
     Status, NetBSD: Supported, Security support external
     Status, OpenBSD: Supported, Security support external
-    Status, Windows: Supported
+    Status, Windows: Supported, with caveats
+
+Windows frontend currently trusts the backend;
+bugs in the frontend which allow backend to cause mischief will not be
+considered security vulnerabilities.
 
 ### PV Framebuffer (frontend)
 
 Guest-side driver capable of speaking the Xen PV Framebuffer protocol
 
-    Status, Linux (xen-fbfront): Supported
+    Status, Linux (xen-fbfront): Supported, with caveats
+
+Linux frontend currently trusts the backend;
+bugs in the frontend which allow backend to cause mischief will not be
+considered security vulnerabilities.
 
 ### PV display (frontend)
 
 Guest-side driver capable of speaking the Xen PV display protocol
 
-    Status, Linux: Supported (outside of "backend allocation" mode)
-    Status, Linux: Experimental (in "backend allocation" mode)
+    Status, Linux, outside of "backend allocation" mode: Supported, with 
caveats
+    Status, Linux, "backend allocation" mode: Experimental
+
+Linux frontend currently trusts the backend;
+bugs in the frontend which allow backend to cause mischief will not be
+considered security vulnerabilities.
 
 ### PV Console (frontend)
 
@@ -449,7 +465,11 @@ Guest-side driver capable of speaking the Xen PV console 
protocol
     Status, Linux (hvc_xen): Supported
     Status, FreeBSD: Supported, Security support external
     Status, NetBSD: Supported, Security support external
-    Status, Windows: Supported
+    Status, Windows: Supported, with caveats
+
+Windows frontend currently trusts the backend;
+bugs in the frontend which allow backend to cause mischief will not be
+considered security vulnerabilities.
 
 ### PV keyboard (frontend)
 
@@ -457,11 +477,19 @@ Guest-side driver capable of speaking the Xen PV keyboard 
protocol.
 Note that the "keyboard protocol" includes mouse / pointer /
 multi-touch support as well.
 
-    Status, Linux (xen-kbdfront): Supported
+    Status, Linux (xen-kbdfront): Supported, with caveats
+
+Linux frontend currently trusts the backend;
+bugs in the frontend which allow backend to cause mischief will not be
+considered security vulnerabilities.
 
 ### PV USB (frontend)
 
-    Status, Linux: Supported
+    Status, Linux: Supported, with caveats
+
+Linux frontend currently trusts the backend;
+bugs in the frontend which allow backend to cause mischief will not be
+considered security vulnerabilities.
 
 ### PV SCSI protocol (frontend)
 
@@ -470,6 +498,10 @@ multi-touch support as well.
 NB that while the PV SCSI frontend is in Linux and tested regularly,
 there is currently no xl support.
 
+Linux frontend currently trusts the backend;
+bugs in the frontend which allow backend to cause mischief will not be
+considered security vulnerabilities.
+
 ### PV TPM (frontend)
 
 Guest-side driver capable of speaking the Xen PV TPM protocol
@@ -492,7 +524,11 @@ Guest-side driver capable of making pv system calls
 
 Guest-side driver capable of speaking the Xen PV sound protocol
 
-    Status, Linux: Supported
+    Status, Linux: Supported, with caveats
+
+Linux frontend currently trusts the backend;
+bugs in the frontend which allow backend to cause mischief will not be
+considered security vulnerabilities.
 
 ## Virtual device support, host side
 
@@ -993,6 +1029,9 @@ are given the following labels:
 
     This feature is security supported
     by a different organization (not the XenProject).
+    The extent of support is defined by that organization.
+    It might be limited, e.g. like described in **Supported, with caveats**
+    below.
     See **External security support** below.
 
   * **Supported, with caveats**
--
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