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From: Kashyap Chamarthy <kchamart@redhat.com>
To: qemu-devel@nongnu.org
Cc: maz@kernel.org, Joel Stanley <joel@jms.id.au>,
Ninad Palsule <ninad@linux.ibm.com>, qemu-arm@nongnu.org,
Andrew Jeffery <andrew@codeconstruct.com.au>,
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Troy Lee <leetroy@gmail.com>, Alistair Francis <alistair@alistair23.me>,
Kashyap Chamarthy <kchamart@redhat.com>
Subject: [PATCH v2 2/3] docs/cpu-features: Update "PAuth" (Pointer
Authentication) details
Date: Thu, 13 Feb 2025 14:50:30 +0100
Message-ID: <20250213135032.2987289-3-kchamart@redhat.com>
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PAuth (Pointer Authentication), a security feature in software, is
relevant for both KVM and QEMU. Relect this fact into the docs:
- For KVM, `pauth` is a binary, "on" vs "off" option. The host CPU
will choose the cryptographic algorithm.
- For TCG, however, along with `pauth`, a couple of properties can be
controlled -- they're are related to cryptographic algorithm choice.
Thanks to Peter Maydell and Marc Zyngier for explaining more about PAuth
on IRC (#qemu, OFTC).
Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com>
Reviewed-by: Alex Benn=C3=A9e <alex.bennee@linaro.org>
---
v2: address Marc Zyngier's comments:
https://lists.gnu.org/archive/html/qemu-devel/2025-01/msg03451.html
---
docs/system/arm/cpu-features.rst | 46 +++++++++++++++++++++++++++++---
1 file changed, 42 insertions(+), 4 deletions(-)
diff --git a/docs/system/arm/cpu-features.rst b/docs/system/arm/cpu-feature=
s.rst
index a596316384..94d260b573 100644
--- a/docs/system/arm/cpu-features.rst
+++ b/docs/system/arm/cpu-features.rst
@@ -204,11 +204,49 @@ the list of KVM vCPU features and their descriptions.
the guest scheduler behavior and/or be exposed to the guest
userspace.
=20
-TCG vCPU Features
-=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
+"PAuth" (Pointer Authentication)
+=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D
+
+PAuth (Pointer Authentication) is a security feature in software that
+was introduced in Armv8.3-A. It aims to protect against ROP
+(return-oriented programming) attacks.
+
+KVM
+---
+
+``pauth``
+
+ Enable or disable ``FEAT_Pauth``. No other properties can be
+ controlled.
+
+ The host CPU will define the PAC (pointer authentication
+ code) cryptographic algorithm.
+
+ There are different "levels" of PAuth support. The host CPU
+ definition will define that level (e.g. PAuth, EPAC, PAuth2, FPAC,
+ FPACCOMBINE, etc). Refer to the Arm architecture extension documents
+ for details about the description of these features.
+
+Live migration and PAuth
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+The level of PAuth support depends on which Arm architecture a given CPU
+supports (e.g. Armv8.3 vs. Armv8.6). This gradation in PAuth support
+has implications for live migration. For example, to be able to
+live-migrate from host-A (with Armv8.3) to host-B (with Arm v8.6):
+
+ - the source and destination hosts must "agree" on (a) the PAC
+ signature algorithm, and (b) all the sub-features of PAuth; or
+
+ - the alternative (and less desirable) option is to turn off PAuth
+ off on both source and destination \ufffd\ufffd\ufffd this is generall=
y not
+ recommended, as PAuth is a security feature.
+
+TCG
+---
=20
-TCG vCPU features are CPU features that are specific to TCG.
-Below is the list of TCG vCPU features and their descriptions.
+For TCG, along with ``pauth``, it is possible to control a few other
+properties of PAuth:
=20
``pauth``
Enable or disable ``FEAT_Pauth`` entirely.
--=20
2.48.1