diff options
| author | Fuad Tabba <tabba@google.com> | 2026-01-22 11:22:16 +0000 |
|---|---|---|
| committer | Marc Zyngier <maz@kernel.org> | 2026-01-23 11:28:48 +0000 |
| commit | f35abcbb8a084db4c24b66ccc8db0405c08e2f61 (patch) | |
| tree | c9553349a7e4143dc841c644ba8b1888f7dd4215 /arch | |
| parent | c103c2dfe4975da31b67a0fcb95761359f30992d (diff) | |
KVM: arm64: Trap MTE access and discovery when MTE is disabled
If MTE is not supported by the hardware, or is disabled in the kernel
configuration (`CONFIG_ARM64_MTE=n`) or command line (`arm64.nomte`),
the kernel stops advertising MTE to userspace and avoids using MTE
instructions. However, this is a software-level disable only.
When MTE hardware is present and enabled by EL3 firmware, leaving
`HCR_EL2.ATA` set allows the host to execute MTE instructions (STG, LDG,
etc.) and access allocation tags in physical memory.
Prevent this by clearing `HCR_EL2.ATA` when MTE is disabled. Remove it
from the `HCR_HOST_NVHE_FLAGS` default, and conditionally set it in
`cpu_prepare_hyp_mode()` only when `system_supports_mte()` returns true.
This causes MTE instructions to trap to EL2 when `HCR_EL2.ATA` is
cleared.
Additionally, set `HCR_EL2.TID5` when MTE is disabled. This traps reads
of `GMID_EL1` (Multiple tag transfer ID register) to EL2, preventing the
discovery of MTE parameters (such as tag block size) when the feature is
suppressed.
Early boot code in `head.S` temporarily keeps `HCR_ATA` set to avoid
special-casing initialization paths. This is safe because this code
executes before untrusted code runs and will clear `HCR_ATA` if MTE is
disabled.
Signed-off-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260122112218.531948-3-tabba@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/arm64/include/asm/kvm_arm.h | 2 | ||||
| -rw-r--r-- | arch/arm64/kernel/head.S | 2 | ||||
| -rw-r--r-- | arch/arm64/kvm/arm.c | 6 |
3 files changed, 8 insertions, 2 deletions
diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h index e500600e4b9b..752e3e1604e8 100644 --- a/arch/arm64/include/asm/kvm_arm.h +++ b/arch/arm64/include/asm/kvm_arm.h @@ -101,7 +101,7 @@ HCR_BSU_IS | HCR_FB | HCR_TACR | \ HCR_AMO | HCR_SWIO | HCR_TIDCP | HCR_RW | HCR_TLOR | \ HCR_FMO | HCR_IMO | HCR_PTW | HCR_TID3 | HCR_TID1) -#define HCR_HOST_NVHE_FLAGS (HCR_RW | HCR_API | HCR_APK | HCR_ATA) +#define HCR_HOST_NVHE_FLAGS (HCR_RW | HCR_API | HCR_APK) #define HCR_HOST_NVHE_PROTECTED_FLAGS (HCR_HOST_NVHE_FLAGS | HCR_TSC) #define HCR_HOST_VHE_FLAGS (HCR_RW | HCR_TGE | HCR_E2H | HCR_AMO | HCR_IMO | HCR_FMO) diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index ca04b338cb0d..87a822e5c4ca 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -299,7 +299,7 @@ SYM_INNER_LABEL(init_el2, SYM_L_LOCAL) isb 0: - init_el2_hcr HCR_HOST_NVHE_FLAGS + init_el2_hcr HCR_HOST_NVHE_FLAGS | HCR_ATA init_el2_state /* Hypervisor stub */ diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index 4f80da0c0d1d..aeac113e5e74 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -2044,6 +2044,12 @@ static void __init cpu_prepare_hyp_mode(int cpu, u32 hyp_va_bits) params->hcr_el2 = HCR_HOST_NVHE_PROTECTED_FLAGS; else params->hcr_el2 = HCR_HOST_NVHE_FLAGS; + + if (system_supports_mte()) + params->hcr_el2 |= HCR_ATA; + else + params->hcr_el2 |= HCR_TID5; + if (cpus_have_final_cap(ARM64_KVM_HVHE)) params->hcr_el2 |= HCR_E2H; params->vttbr = params->vtcr = 0; |