diff options
Diffstat (limited to 'Documentation/arm64')
| -rw-r--r-- | Documentation/arm64/booting.rst | 13 | ||||
| -rw-r--r-- | Documentation/arm64/pointer-authentication.rst | 34 | ||||
| -rw-r--r-- | Documentation/arm64/tagged-address-abi.rst | 2 |
3 files changed, 45 insertions, 4 deletions
diff --git a/Documentation/arm64/booting.rst b/Documentation/arm64/booting.rst index 7552dbc1cc54..4fcc00add117 100644 --- a/Documentation/arm64/booting.rst +++ b/Documentation/arm64/booting.rst @@ -202,9 +202,10 @@ Before jumping into the kernel, the following conditions must be met: - System registers - All writable architected system registers at the exception level where - the kernel image will be entered must be initialised by software at a - higher exception level to prevent execution in an UNKNOWN state. + All writable architected system registers at or below the exception + level where the kernel image will be entered must be initialised by + software at a higher exception level to prevent execution in an UNKNOWN + state. - SCR_EL3.FIQ must have the same value across all CPUs the kernel is executing on. @@ -270,6 +271,12 @@ Before jumping into the kernel, the following conditions must be met: having 0b1 set for the corresponding bit for each of the auxiliary counters present. + For CPUs with the Fine Grained Traps (FEAT_FGT) extension present: + + - If EL3 is present and the kernel is entered at EL2: + + - SCR_EL3.FGTEn (bit 27) must be initialised to 0b1. + The requirements described above for CPU mode, caches, MMUs, architected timers, coherency and system registers apply to all CPUs. All CPUs must enter the kernel in the same exception level. 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. diff --git a/Documentation/arm64/tagged-address-abi.rst b/Documentation/arm64/tagged-address-abi.rst index 4a9d9c794ee5..cbc4d4500241 100644 --- a/Documentation/arm64/tagged-address-abi.rst +++ b/Documentation/arm64/tagged-address-abi.rst @@ -40,7 +40,7 @@ space obtained in one of the following ways: during creation and with the same restrictions as for ``mmap()`` above (e.g. data, bss, stack). -The AArch64 Tagged Address ABI has two stages of relaxation depending +The AArch64 Tagged Address ABI has two stages of relaxation depending on how the user addresses are used by the kernel: 1. User addresses not accessed by the kernel but used for address space |