| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <4e475e1f-80f2-372a-2c16-a03ac947525a@arm.com>
Date: Wed, 24 Apr 2019 15:29:26 +0100
From: Marc Zyngier <marc.zyngier@....com>
To: Dave Martin <Dave.Martin@....com>,
Amit Daniel Kachhap <amit.kachhap@....com>
Cc: linux-arm-kernel@...ts.infradead.org,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
Kristina Martsenko <kristina.martsenko@....com>,
kvmarm@...ts.cs.columbia.edu,
Ramana Radhakrishnan <ramana.radhakrishnan@....com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 2/5] KVM: arm/arm64: context-switch ptrauth registers
On 24/04/2019 14:39, Dave Martin wrote:
> On Tue, Apr 23, 2019 at 10:12:35AM +0530, Amit Daniel Kachhap wrote:
>> From: Mark Rutland <mark.rutland@....com>
>>
>> When pointer authentication is supported, a guest may wish to use it.
>> This patch adds the necessary KVM infrastructure for this to work, with
>> a semi-lazy context switch of the pointer auth state.
>>
>> Pointer authentication feature is only enabled when VHE is built
>> in the kernel and present in the CPU implementation so only VHE code
>> paths are modified.
>>
>> When we schedule a vcpu, we disable guest usage of pointer
>> authentication instructions and accesses to the keys. While these are
>> disabled, we avoid context-switching the keys. When we trap the guest
>> trying to use pointer authentication functionality, we change to eagerly
>> context-switching the keys, and enable the feature. The next time the
>> vcpu is scheduled out/in, we start again. However the host key save is
>> optimized and implemented inside ptrauth instruction/register access
>> trap.
>>
>> Pointer authentication consists of address authentication and generic
>> authentication, and CPUs in a system might have varied support for
>> either. Where support for either feature is not uniform, it is hidden
>> from guests via ID register emulation, as a result of the cpufeature
>> framework in the host.
>>
>> Unfortunately, address authentication and generic authentication cannot
>> be trapped separately, as the architecture provides a single EL2 trap
>> covering both. If we wish to expose one without the other, we cannot
>> prevent a (badly-written) guest from intermittently using a feature
>> which is not uniformly supported (when scheduled on a physical CPU which
>> supports the relevant feature). Hence, this patch expects both type of
>> authentication to be present in a cpu.
>>
>> This switch of key is done from guest enter/exit assembly as preparation
>> for the upcoming in-kernel pointer authentication support. Hence, these
>> key switching routines are not implemented in C code as they may cause
>> pointer authentication key signing error in some situations.
>>
>> Signed-off-by: Mark Rutland <mark.rutland@....com>
>> [Only VHE, key switch in full assembly, vcpu_has_ptrauth checks
>> , save host key in ptrauth exception trap]
>> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@....com>
>> Reviewed-by: Julien Thierry <julien.thierry@....com>
>> Cc: Marc Zyngier <marc.zyngier@....com>
>> Cc: Christoffer Dall <christoffer.dall@....com>
>> Cc: kvmarm@...ts.cs.columbia.edu
>> ---
>> Changes since v9:
>>
>> * Removed hardcoding of enum values[Mark Zyngier].
>> * Changed kvm_ptrauth_asm.h to kvm_ptrauth.h[Mark Zyngier].
>> * Removed macro __ptrauth_save_state and applied inline [Marc Zyngier].
>> * Moved kvm_arm_vcpu_ptrauth_setup_lazy, kvm_arm_vcpu_ptrauth_enable and
>> kvm_arm_vcpu_ptrauth_disable from *.c to kvm_emulate.h file [Marc Zyngier].
>> * Added/Modified comments at few places [Marc Zyngier].
>
> [...]
>
>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>
> [...]
>
>> @@ -1058,9 +1087,11 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
>> (0xfUL << ID_AA64ISAR1_API_SHIFT) |
>> (0xfUL << ID_AA64ISAR1_GPA_SHIFT) |
>> (0xfUL << ID_AA64ISAR1_GPI_SHIFT);
>> - if (val & ptrauth_mask)
>> - kvm_debug("ptrauth unsupported for guests, suppressing\n");
>> - val &= ~ptrauth_mask;
>> + if (!vcpu_has_ptrauth(vcpu)) {
>> + if (val & ptrauth_mask)
>> + kvm_debug("ptrauth unsupported for guests, suppressing\n");
>> + val &= ~ptrauth_mask;
>> + }
>
> Hmmm, didn't spot this before, but this error message no longer makes
> sense now that KVM _does_ support pointer auth.
>
> Without vcpu_has_ptrauth(vcpu), we should just silently mask out the
> relevant ID fields now (same as for SVE).
>
> The patch below should achieve that.
>
> --8<--
>
> From c6065122c5cccef57108dff990ce8fb43426f88e Mon Sep 17 00:00:00 2001
> From: Dave Martin <Dave.Martin@....com>
> Date: Wed, 24 Apr 2019 14:32:29 +0100
> Subject: [PATCH] KVM: arm64: sys_regs: Remove warning about missing pointer
> auth support
>
> KVM does support pointer auth for guests now, so it is
> inappropriate (and confusing) to print a warning to dmesg when
> userspace explicitly does not ask for pointer auth to be turned on
> for a vcpu.
>
> So, just squash the virtual ptrauth ID_AA64ISAR1_EL1 fields when
> appropriate and remove the warning.
>
> Signed-off-by: Dave Martin <Dave.Martin@....com>
> ---
> arch/arm64/kvm/sys_regs.c | 15 +++++----------
> 1 file changed, 5 insertions(+), 10 deletions(-)
>
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 7f06c2e..f599f5e 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1082,16 +1082,11 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
>
> if (id == SYS_ID_AA64PFR0_EL1 && !vcpu_has_sve(vcpu)) {
> val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT);
> - } else if (id == SYS_ID_AA64ISAR1_EL1) {
> - const u64 ptrauth_mask = (0xfUL << ID_AA64ISAR1_APA_SHIFT) |
> - (0xfUL << ID_AA64ISAR1_API_SHIFT) |
> - (0xfUL << ID_AA64ISAR1_GPA_SHIFT) |
> - (0xfUL << ID_AA64ISAR1_GPI_SHIFT);
> - if (!vcpu_has_ptrauth(vcpu)) {
> - if (val & ptrauth_mask)
> - kvm_debug("ptrauth unsupported for guests, suppressing\n");
> - val &= ~ptrauth_mask;
> - }
> + } else if (id == SYS_ID_AA64ISAR1_EL1 && !vcpu_has_ptrauth(vcpu)) {
> + val &= ~((0xfUL << ID_AA64ISAR1_APA_SHIFT) |
> + (0xfUL << ID_AA64ISAR1_API_SHIFT) |
> + (0xfUL << ID_AA64ISAR1_GPA_SHIFT) |
> + (0xfUL << ID_AA64ISAR1_GPI_SHIFT));
> }
>
> return val;
>
Since the series isn't in -next yet, I've squashed the above with the
other nits I had in -queue.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
Powered by blists - more mailing lists