| f396aec8 | 09-Sep-2025 |
Arvind Ram Prakash <arvind.ramprakash@arm.com> |
feat(cpufeat): add support for FEAT_IDTE3
This patch adds support for FEAT_IDTE3, which introduces support for handling the trapping of Group 3 and Group 5 (only GMID_EL1) registers to EL3 (unless t
feat(cpufeat): add support for FEAT_IDTE3
This patch adds support for FEAT_IDTE3, which introduces support for handling the trapping of Group 3 and Group 5 (only GMID_EL1) registers to EL3 (unless trapped to EL2). IDTE3 allows EL3 to modify the view of ID registers for lower ELs, and this capability is used to disable fields of ID registers tied to disabled features.
The ID registers are initially read as-is and stored in context. Then, based on the feature enablement status for each world, if a particular feature is disabled, its corresponding field in the cached ID register is set to Res0. When lower ELs attempt to read an ID register, the cached ID register value is returned. This allows EL3 to prevent lower ELs from accessing feature-specific system registers that are disabled in EL3, even though the hardware implements them.
The emulated ID register values are stored primarily in per-world context, except for certain debug-related ID registers such as ID_AA64DFR0_EL1 and ID_AA64DFR1_EL1, which are stored in the cpu_data and are unique to each PE. This is done to support feature asymmetry that is commonly seen in debug features.
FEAT_IDTE3 traps all Group 3 ID registers in the range op0 == 3, op1 == 0, CRn == 0, CRm == {2–7}, op2 == {0–7} and the Group 5 GMID_EL1 register. However, only a handful of ID registers contain fields used to detect features enabled in EL3. Hence, we only cache those ID registers, while the rest are transparently returned as is to the lower EL.
This patch updates the CREATE_FEATURE_FUNCS macro to generate update_feat_xyz_idreg_field() functions that disable ID register fields on a per-feature basis. The enabled_worlds scope is used to disable ID register fields for security states where the feature is not enabled.
This EXPERIMENTAL feature is controlled by the ENABLE_FEAT_IDTE3 build flag and is currently disabled by default.
Signed-off-by: Arvind Ram Prakash <arvind.ramprakash@arm.com> Change-Id: I5f998eeab81bb48c7595addc5595313a9ebb96d5
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| 1ae75529 | 21-Nov-2022 |
Andre Przywara <andre.przywara@arm.com> |
feat(fvp): emulate trapped RNDR
When a platform decides to use FEAT_RNG_TRAP, every RNDR or RNDRSS read will trap into EL3. The platform can then emulate those instructions, by either executing the
feat(fvp): emulate trapped RNDR
When a platform decides to use FEAT_RNG_TRAP, every RNDR or RNDRSS read will trap into EL3. The platform can then emulate those instructions, by either executing the real CPU instructions, potentially conditioning the results, or use rate-limiting or filtering to protect the hardware entropy pool. Another possiblitiy would be to use some platform specific TRNG device to get entropy and returning this.
To demonstrate platform specific usage, add a demo implementation for the FVP: It will execute the actual CPU instruction and just return the result. This should serve as reference code to implement platform specific policies.
We change the definition of read_rndr() and read_rndrrs() to use the alternative sysreg encoding, so that all assemblers can handle that.
Add documentation about the new platform specific RNG handler function.
Signed-off-by: Andre Przywara <andre.przywara@arm.com> Change-Id: Ibce817b3b06ad20129d15531b81402e3cc3e9a9e
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