From: Andrew Scull <ascull@google.com> To: Mark Rutland <mark.rutland@arm.com> Cc: Marc Zyngier <maz@kernel.org>, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, James Morse <james.morse@arm.com>, Julien Thierry <julien.thierry.kdev@gmail.com>, Suzuki K Poulose <suzuki.poulose@arm.com>, Dave Martin <Dave.Martin@arm.com>, kernel-team@android.com Subject: Re: [PATCH v2 5/5] KVM: arm64: Simplify PtrAuth alternative patching Date: Mon, 22 Jun 2020 11:39:32 +0100 [thread overview] Message-ID: <20200622103932.GA178085@google.com> (raw) In-Reply-To: <20200622091508.GB88608@C02TD0UTHF1T.local> On Mon, Jun 22, 2020 at 10:15:08AM +0100, Mark Rutland wrote: > On Mon, Jun 22, 2020 at 09:06:43AM +0100, Marc Zyngier wrote: > > --- a/arch/arm64/include/asm/kvm_ptrauth.h > > +++ b/arch/arm64/include/asm/kvm_ptrauth.h > > @@ -61,44 +61,36 @@ > > > > /* > > * Both ptrauth_switch_to_guest and ptrauth_switch_to_host macros will > > - * check for the presence of one of the cpufeature flag > > - * ARM64_HAS_ADDRESS_AUTH_ARCH or ARM64_HAS_ADDRESS_AUTH_IMP_DEF and > > + * check for the presence ARM64_HAS_ADDRESS_AUTH, which is defined as > > + * (ARM64_HAS_ADDRESS_AUTH_ARCH || ARM64_HAS_ADDRESS_AUTH_IMP_DEF) and > > * then proceed ahead with the save/restore of Pointer Authentication > > - * key registers. > > + * key registers if enabled for the guest. > > */ > > .macro ptrauth_switch_to_guest g_ctxt, reg1, reg2, reg3 > > -alternative_if ARM64_HAS_ADDRESS_AUTH_ARCH > > +alternative_if_not ARM64_HAS_ADDRESS_AUTH > > b 1000f > > alternative_else_nop_endif > > -alternative_if_not ARM64_HAS_ADDRESS_AUTH_IMP_DEF > > - b 1001f > > -alternative_else_nop_endif > > -1000: > > mrs \reg1, hcr_el2 > > and \reg1, \reg1, #(HCR_API | HCR_APK) > > - cbz \reg1, 1001f > > + cbz \reg1, 1000f > > add \reg1, \g_ctxt, #CPU_APIAKEYLO_EL1 > > ptrauth_restore_state \reg1, \reg2, \reg3 > > -1001: > > +1000: > > .endm > > Since these are in macros, we could use \@ to generate a macro-specific > lavel rather than a magic number, which would be less likely to conflict > with the surrounding environment and would be more descriptive. We do > that in a few places already, and here it could look something like: > > | alternative_if_not ARM64_HAS_ADDRESS_AUTH > | b .L__skip_pauth_switch\@ > | alternative_else_nop_endif > | > | ... > | > | .L__skip_pauth_switch\@: > > Per the gas documentation > > | \@ > | > | as maintains a counter of how many macros it has executed in this > | pseudo-variable; you can copy that number to your output with ‘\@’, > | but only within a macro definition. Is this relibale for this sort of application? The description just sounds like a counter of macros rather than specifically a unique label generator. It may work most of the time but also seems that it has the potential to be more fragile given that it would change based on the rest of the code in the file to potentially conflict with something it didn't previously conflict with.
WARNING: multiple messages have this Message-ID (diff)
From: Andrew Scull <ascull@google.com> To: Mark Rutland <mark.rutland@arm.com> Cc: kvm@vger.kernel.org, Marc Zyngier <maz@kernel.org>, Dave Martin <Dave.Martin@arm.com>, linux-arm-kernel@lists.infradead.org, kernel-team@android.com, kvmarm@lists.cs.columbia.edu Subject: Re: [PATCH v2 5/5] KVM: arm64: Simplify PtrAuth alternative patching Date: Mon, 22 Jun 2020 11:39:32 +0100 [thread overview] Message-ID: <20200622103932.GA178085@google.com> (raw) In-Reply-To: <20200622091508.GB88608@C02TD0UTHF1T.local> On Mon, Jun 22, 2020 at 10:15:08AM +0100, Mark Rutland wrote: > On Mon, Jun 22, 2020 at 09:06:43AM +0100, Marc Zyngier wrote: > > --- a/arch/arm64/include/asm/kvm_ptrauth.h > > +++ b/arch/arm64/include/asm/kvm_ptrauth.h > > @@ -61,44 +61,36 @@ > > > > /* > > * Both ptrauth_switch_to_guest and ptrauth_switch_to_host macros will > > - * check for the presence of one of the cpufeature flag > > - * ARM64_HAS_ADDRESS_AUTH_ARCH or ARM64_HAS_ADDRESS_AUTH_IMP_DEF and > > + * check for the presence ARM64_HAS_ADDRESS_AUTH, which is defined as > > + * (ARM64_HAS_ADDRESS_AUTH_ARCH || ARM64_HAS_ADDRESS_AUTH_IMP_DEF) and > > * then proceed ahead with the save/restore of Pointer Authentication > > - * key registers. > > + * key registers if enabled for the guest. > > */ > > .macro ptrauth_switch_to_guest g_ctxt, reg1, reg2, reg3 > > -alternative_if ARM64_HAS_ADDRESS_AUTH_ARCH > > +alternative_if_not ARM64_HAS_ADDRESS_AUTH > > b 1000f > > alternative_else_nop_endif > > -alternative_if_not ARM64_HAS_ADDRESS_AUTH_IMP_DEF > > - b 1001f > > -alternative_else_nop_endif > > -1000: > > mrs \reg1, hcr_el2 > > and \reg1, \reg1, #(HCR_API | HCR_APK) > > - cbz \reg1, 1001f > > + cbz \reg1, 1000f > > add \reg1, \g_ctxt, #CPU_APIAKEYLO_EL1 > > ptrauth_restore_state \reg1, \reg2, \reg3 > > -1001: > > +1000: > > .endm > > Since these are in macros, we could use \@ to generate a macro-specific > lavel rather than a magic number, which would be less likely to conflict > with the surrounding environment and would be more descriptive. We do > that in a few places already, and here it could look something like: > > | alternative_if_not ARM64_HAS_ADDRESS_AUTH > | b .L__skip_pauth_switch\@ > | alternative_else_nop_endif > | > | ... > | > | .L__skip_pauth_switch\@: > > Per the gas documentation > > | \@ > | > | as maintains a counter of how many macros it has executed in this > | pseudo-variable; you can copy that number to your output with ‘\@’, > | but only within a macro definition. Is this relibale for this sort of application? The description just sounds like a counter of macros rather than specifically a unique label generator. It may work most of the time but also seems that it has the potential to be more fragile given that it would change based on the rest of the code in the file to potentially conflict with something it didn't previously conflict with. _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
next prev parent reply other threads:[~2020-06-22 10:39 UTC|newest] Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-06-22 8:06 [PATCH v2 0/5] KVM/arm64: Enable PtrAuth on non-VHE KVM Marc Zyngier 2020-06-22 8:06 ` Marc Zyngier 2020-06-22 8:06 ` [PATCH v2 1/5] KVM: arm64: Enable Address Authentication at EL2 if available Marc Zyngier 2020-06-22 8:06 ` Marc Zyngier 2020-06-22 9:04 ` Mark Rutland 2020-06-22 9:04 ` Mark Rutland 2020-06-22 8:06 ` [PATCH v2 2/5] KVM: arm64: Allow ARM64_PTR_AUTH when ARM64_VHE=n Marc Zyngier 2020-06-22 8:06 ` Marc Zyngier 2020-06-22 8:06 ` [PATCH v2 3/5] KVM: arm64: Allow PtrAuth to be enabled from userspace on non-VHE systems Marc Zyngier 2020-06-22 8:06 ` Marc Zyngier 2020-06-22 8:06 ` [PATCH v2 4/5] KVM: arm64: Check HCR_EL2 instead of shadow copy to swap PtrAuth registers Marc Zyngier 2020-06-22 8:06 ` Marc Zyngier 2020-06-22 8:06 ` [PATCH v2 5/5] KVM: arm64: Simplify PtrAuth alternative patching Marc Zyngier 2020-06-22 8:06 ` Marc Zyngier 2020-06-22 9:15 ` Mark Rutland 2020-06-22 9:15 ` Mark Rutland 2020-06-22 10:25 ` Marc Zyngier 2020-06-22 10:25 ` Marc Zyngier 2020-06-22 10:31 ` Mark Rutland 2020-06-22 10:31 ` Mark Rutland 2020-06-22 10:39 ` Andrew Scull [this message] 2020-06-22 10:39 ` Andrew Scull 2020-06-22 10:43 ` Andrew Scull 2020-06-22 10:43 ` Andrew Scull
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