[2/2] docs/cpu-features: Update "PAuth" (Pointer Authentication) details

Commit Message

Kashyap Chamarthy Jan. 17, 2025, 7:11 p.m. UTC

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 <[e-mail]>
---
 docs/system/arm/cpu-features.rst | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

Patch

diff --git a/docs/system/arm/cpu-features.rst b/docs/system/arm/cpu-features.rst
index 78f18c87a81..7f99f7614b4 100644
--- a/docs/system/arm/cpu-features.rst
+++ b/docs/system/arm/cpu-features.rst
@@ -204,11 +204,26 @@  the list of KVM vCPU features and their descriptions.
   the guest scheduler behavior and/or be exposed to the guest
   userspace.
 
-TCG vCPU Features
-=================
+"PAuth" (Pointer Authentication)
+================================
+
+PAuth (Pointer Authentication) is a security feature in software that
+was introduced in Armv8.3-A and Armv9.0-A.  It aims to protect against
+ROP (return-oriented programming) attacks.
+
+KVM
+---
+
+``pauth``
+
+  Enable or disable ``FEAT_Pauth``.  The host silicon will choose the
+  cryptographic algorithm.  No other properties can be controlled.
+
+TCG
+---
 
-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:
 
 ``pauth``
   Enable or disable ``FEAT_Pauth`` entirely.