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author | Catalin Marinas <catalin.marinas@arm.com> | 2021-04-15 16:00:48 +0300 |
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committer | Catalin Marinas <catalin.marinas@arm.com> | 2021-04-15 16:00:48 +0300 |
commit | a27a8816568964fcef62a3ae5f9d2228ec1ebc68 (patch) | |
tree | 7197c94bcf5b600bb43e7aa70ba2b05a7fb82cd1 /Documentation | |
parent | 604df13d7aadae6902d3b7f03a35bb21d887f0cf (diff) | |
parent | b90e483938ce387c256e03fb144f82f64551847b (diff) | |
download | linux-a27a8816568964fcef62a3ae5f9d2228ec1ebc68.tar.xz |
Merge branch 'for-next/pac-set-get-enabled-keys' into for-next/core
* for-next/pac-set-get-enabled-keys:
: Introduce arm64 prctl(PR_PAC_{SET,GET}_ENABLED_KEYS).
arm64: pac: Optimize kernel entry/exit key installation code paths
arm64: Introduce prctl(PR_PAC_{SET,GET}_ENABLED_KEYS)
arm64: mte: make the per-task SCTLR_EL1 field usable elsewhere
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/arm64/pointer-authentication.rst | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/Documentation/arm64/pointer-authentication.rst b/Documentation/arm64/pointer-authentication.rst index 30b2ab06526b..f127666ea3a8 100644 --- a/Documentation/arm64/pointer-authentication.rst +++ b/Documentation/arm64/pointer-authentication.rst @@ -107,3 +107,37 @@ filter out the Pointer Authentication system key registers from KVM_GET/SET_REG_* ioctls and mask those features from cpufeature ID register. Any attempt to use the Pointer Authentication instructions will result in an UNDEFINED exception being injected into the guest. + + +Enabling and disabling keys +--------------------------- + +The prctl PR_PAC_SET_ENABLED_KEYS allows the user program to control which +PAC keys are enabled in a particular task. It takes two arguments, the +first being a bitmask of PR_PAC_APIAKEY, PR_PAC_APIBKEY, PR_PAC_APDAKEY +and PR_PAC_APDBKEY specifying which keys shall be affected by this prctl, +and the second being a bitmask of the same bits specifying whether the key +should be enabled or disabled. For example:: + + prctl(PR_PAC_SET_ENABLED_KEYS, + PR_PAC_APIAKEY | PR_PAC_APIBKEY | PR_PAC_APDAKEY | PR_PAC_APDBKEY, + PR_PAC_APIBKEY, 0, 0); + +disables all keys except the IB key. + +The main reason why this is useful is to enable a userspace ABI that uses PAC +instructions to sign and authenticate function pointers and other pointers +exposed outside of the function, while still allowing binaries conforming to +the ABI to interoperate with legacy binaries that do not sign or authenticate +pointers. + +The idea is that a dynamic loader or early startup code would issue this +prctl very early after establishing that a process may load legacy binaries, +but before executing any PAC instructions. + +For compatibility with previous kernel versions, processes start up with IA, +IB, DA and DB enabled, and are reset to this state on exec(). Processes created +via fork() and clone() inherit the key enabled state from the calling process. + +It is recommended to avoid disabling the IA key, as this has higher performance +overhead than disabling any of the other keys. |