diff mbox series

[v3] arm64: Filter out SVE hwcaps when FEAT_SVE isn't implemented

Message ID 20250106174020.1793678-1-maz@kernel.org (mailing list archive)
State New
Headers show
Series [v3] arm64: Filter out SVE hwcaps when FEAT_SVE isn't implemented | expand

Commit Message

Marc Zyngier Jan. 6, 2025, 5:40 p.m. UTC 
The hwcaps code that exposes SVE features to userspace only
considers ID_AA64ZFR0_EL1, while this is only valid when
ID_AA64PFR0_EL1.SVE advertises that SVE is actually supported.

The expectations are that when ID_AA64PFR0_EL1.SVE is 0, the
ID_AA64ZFR0_EL1 register is also 0. So far, so good.

Things become a bit more interesting if the HW implements SME.
In this case, a few ID_AA64ZFR0_EL1 fields indicate *SME*
features. And these fields overlap with their SVE interpretations.
But the architecture says that the SME and SVE feature sets must
match, so we're still hunky-dory.

This goes wrong if the HW implements SME, but not SVE. In this
case, we end-up advertising some SVE features to userspace, even
if the HW has none. That's because we never consider whether SVE
is actually implemented. Oh well.

Fix it by restricting all SVE capabilities to ID_AA64PFR0_EL1.SVE
being non-zero. The HWCAPS documentation is amended to reflect the
actually checks performed by the kernel.

Fixes: 06a916feca2b ("arm64: Expose SVE2 features for userspace")
Reported-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org
---
 Documentation/arch/arm64/elf_hwcaps.rst | 39 ++++++++++++++++--------
 arch/arm64/kernel/cpufeature.c          | 40 +++++++++++++++++--------
 2 files changed, 53 insertions(+), 26 deletions(-)

Comments

Mark Brown Jan. 6, 2025, 7:17 p.m. UTC | #1 
On Mon, Jan 06, 2025 at 05:40:20PM +0000, Marc Zyngier wrote:

> Things become a bit more interesting if the HW implements SME.
> In this case, a few ID_AA64ZFR0_EL1 fields indicate *SME*
> features. And these fields overlap with their SVE interpretations.
> But the architecture says that the SME and SVE feature sets must
> match, so we're still hunky-dory.

> This goes wrong if the HW implements SME, but not SVE. In this
> case, we end-up advertising some SVE features to userspace, even
> if the HW has none. That's because we never consider whether SVE
> is actually implemented. Oh well.

> Fix it by restricting all SVE capabilities to ID_AA64PFR0_EL1.SVE
> being non-zero. The HWCAPS documentation is amended to reflect the
> actually checks performed by the kernel.

Reviewed-by: Mark Brown <broonie@kernel.org>

This is probably our best option here, it's what we really meant anyway
- SME did retroactively complicate the meaning of the fields so it's not
unreasaonable for userspace to get confused.  For SME specific usage we
should implement separate SME capabilities that have a similar has_sme()
check, I'll look into that.

I agree with the discussion on v2 that anything reading the ID registers
from userspace needs to have a similar understanding that SME only
systems exist so we shouldn't do anything there.
diff mbox series

Patch

diff --git a/Documentation/arch/arm64/elf_hwcaps.rst b/Documentation/arch/arm64/elf_hwcaps.rst
index 2ff922a406ad8..1a31723e79fd2 100644
--- a/Documentation/arch/arm64/elf_hwcaps.rst
+++ b/Documentation/arch/arm64/elf_hwcaps.rst
@@ -178,22 +178,28 @@  HWCAP2_DCPODP
     Functionality implied by ID_AA64ISAR1_EL1.DPB == 0b0010.
 
 HWCAP2_SVE2
-    Functionality implied by ID_AA64ZFR0_EL1.SVEver == 0b0001.
+    Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001 and
+    ID_AA64ZFR0_EL1.SVEver == 0b0001.
 
 HWCAP2_SVEAES
-    Functionality implied by ID_AA64ZFR0_EL1.AES == 0b0001.
+    Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001 and
+    ID_AA64ZFR0_EL1.AES == 0b0001.
 
 HWCAP2_SVEPMULL
-    Functionality implied by ID_AA64ZFR0_EL1.AES == 0b0010.
+    Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001 and
+    ID_AA64ZFR0_EL1.AES == 0b0010.
 
 HWCAP2_SVEBITPERM
-    Functionality implied by ID_AA64ZFR0_EL1.BitPerm == 0b0001.
+    Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001 and
+    ID_AA64ZFR0_EL1.BitPerm == 0b0001.
 
 HWCAP2_SVESHA3
-    Functionality implied by ID_AA64ZFR0_EL1.SHA3 == 0b0001.
+    Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001 and
+    ID_AA64ZFR0_EL1.SHA3 == 0b0001.
 
 HWCAP2_SVESM4
-    Functionality implied by ID_AA64ZFR0_EL1.SM4 == 0b0001.
+    Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001 and
+    ID_AA64ZFR0_EL1.SM4 == 0b0001.
 
 HWCAP2_FLAGM2
     Functionality implied by ID_AA64ISAR0_EL1.TS == 0b0010.
@@ -202,16 +208,20 @@  HWCAP2_FRINT
     Functionality implied by ID_AA64ISAR1_EL1.FRINTTS == 0b0001.
 
 HWCAP2_SVEI8MM
-    Functionality implied by ID_AA64ZFR0_EL1.I8MM == 0b0001.
+    Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001 and
+    ID_AA64ZFR0_EL1.I8MM == 0b0001.
 
 HWCAP2_SVEF32MM
-    Functionality implied by ID_AA64ZFR0_EL1.F32MM == 0b0001.
+    Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001 and
+    ID_AA64ZFR0_EL1.F32MM == 0b0001.
 
 HWCAP2_SVEF64MM
-    Functionality implied by ID_AA64ZFR0_EL1.F64MM == 0b0001.
+    Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001 and
+    ID_AA64ZFR0_EL1.F64MM == 0b0001.
 
 HWCAP2_SVEBF16
-    Functionality implied by ID_AA64ZFR0_EL1.BF16 == 0b0001.
+    Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001 and
+    ID_AA64ZFR0_EL1.BF16 == 0b0001.
 
 HWCAP2_I8MM
     Functionality implied by ID_AA64ISAR1_EL1.I8MM == 0b0001.
@@ -277,7 +287,8 @@  HWCAP2_EBF16
     Functionality implied by ID_AA64ISAR1_EL1.BF16 == 0b0010.
 
 HWCAP2_SVE_EBF16
-    Functionality implied by ID_AA64ZFR0_EL1.BF16 == 0b0010.
+    Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001 and
+    ID_AA64ZFR0_EL1.BF16 == 0b0010.
 
 HWCAP2_CSSC
     Functionality implied by ID_AA64ISAR2_EL1.CSSC == 0b0001.
@@ -286,7 +297,8 @@  HWCAP2_RPRFM
     Functionality implied by ID_AA64ISAR2_EL1.RPRFM == 0b0001.
 
 HWCAP2_SVE2P1
-    Functionality implied by ID_AA64ZFR0_EL1.SVEver == 0b0010.
+    Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001 and
+    ID_AA64ZFR0_EL1.SVEver == 0b0010.
 
 HWCAP2_SME2
     Functionality implied by ID_AA64SMFR0_EL1.SMEver == 0b0001.
@@ -313,7 +325,8 @@  HWCAP2_HBC
     Functionality implied by ID_AA64ISAR2_EL1.BC == 0b0001.
 
 HWCAP2_SVE_B16B16
-    Functionality implied by ID_AA64ZFR0_EL1.B16B16 == 0b0001.
+    Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001 and
+    ID_AA64ZFR0_EL1.B16B16 == 0b0001.
 
 HWCAP2_LRCPC3
     Functionality implied by ID_AA64ISAR1_EL1.LRCPC == 0b0011.
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 6ce71f444ed84..6874aca5da9df 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -3022,6 +3022,13 @@  static const struct arm64_cpu_capabilities arm64_features[] = {
 		.matches = match,						\
 	}
 
+#define HWCAP_CAP_MATCH_ID(match, reg, field, min_value, cap_type, cap)		\
+	{									\
+		__HWCAP_CAP(#cap, cap_type, cap)				\
+		HWCAP_CPUID_MATCH(reg, field, min_value) 			\
+		.matches = match,						\
+	}
+
 #ifdef CONFIG_ARM64_PTR_AUTH
 static const struct arm64_cpu_capabilities ptr_auth_hwcap_addr_matches[] = {
 	{
@@ -3050,6 +3057,13 @@  static const struct arm64_cpu_capabilities ptr_auth_hwcap_gen_matches[] = {
 };
 #endif
 
+#ifdef CONFIG_ARM64_SVE
+static bool has_sve_feature(const struct arm64_cpu_capabilities *cap, int scope)
+{
+	return system_supports_sve() && has_user_cpuid_feature(cap, scope);
+}
+#endif
+
 static const struct arm64_cpu_capabilities arm64_elf_hwcaps[] = {
 	HWCAP_CAP(ID_AA64ISAR0_EL1, AES, PMULL, CAP_HWCAP, KERNEL_HWCAP_PMULL),
 	HWCAP_CAP(ID_AA64ISAR0_EL1, AES, AES, CAP_HWCAP, KERNEL_HWCAP_AES),
@@ -3092,19 +3106,19 @@  static const struct arm64_cpu_capabilities arm64_elf_hwcaps[] = {
 	HWCAP_CAP(ID_AA64MMFR2_EL1, AT, IMP, CAP_HWCAP, KERNEL_HWCAP_USCAT),
 #ifdef CONFIG_ARM64_SVE
 	HWCAP_CAP(ID_AA64PFR0_EL1, SVE, IMP, CAP_HWCAP, KERNEL_HWCAP_SVE),
-	HWCAP_CAP(ID_AA64ZFR0_EL1, SVEver, SVE2p1, CAP_HWCAP, KERNEL_HWCAP_SVE2P1),
-	HWCAP_CAP(ID_AA64ZFR0_EL1, SVEver, SVE2, CAP_HWCAP, KERNEL_HWCAP_SVE2),
-	HWCAP_CAP(ID_AA64ZFR0_EL1, AES, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEAES),
-	HWCAP_CAP(ID_AA64ZFR0_EL1, AES, PMULL128, CAP_HWCAP, KERNEL_HWCAP_SVEPMULL),
-	HWCAP_CAP(ID_AA64ZFR0_EL1, BitPerm, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEBITPERM),
-	HWCAP_CAP(ID_AA64ZFR0_EL1, B16B16, IMP, CAP_HWCAP, KERNEL_HWCAP_SVE_B16B16),
-	HWCAP_CAP(ID_AA64ZFR0_EL1, BF16, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEBF16),
-	HWCAP_CAP(ID_AA64ZFR0_EL1, BF16, EBF16, CAP_HWCAP, KERNEL_HWCAP_SVE_EBF16),
-	HWCAP_CAP(ID_AA64ZFR0_EL1, SHA3, IMP, CAP_HWCAP, KERNEL_HWCAP_SVESHA3),
-	HWCAP_CAP(ID_AA64ZFR0_EL1, SM4, IMP, CAP_HWCAP, KERNEL_HWCAP_SVESM4),
-	HWCAP_CAP(ID_AA64ZFR0_EL1, I8MM, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEI8MM),
-	HWCAP_CAP(ID_AA64ZFR0_EL1, F32MM, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEF32MM),
-	HWCAP_CAP(ID_AA64ZFR0_EL1, F64MM, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEF64MM),
+	HWCAP_CAP_MATCH_ID(has_sve_feature, ID_AA64ZFR0_EL1, SVEver, SVE2p1, CAP_HWCAP, KERNEL_HWCAP_SVE2P1),
+	HWCAP_CAP_MATCH_ID(has_sve_feature, ID_AA64ZFR0_EL1, SVEver, SVE2, CAP_HWCAP, KERNEL_HWCAP_SVE2),
+	HWCAP_CAP_MATCH_ID(has_sve_feature, ID_AA64ZFR0_EL1, AES, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEAES),
+	HWCAP_CAP_MATCH_ID(has_sve_feature, ID_AA64ZFR0_EL1, AES, PMULL128, CAP_HWCAP, KERNEL_HWCAP_SVEPMULL),
+	HWCAP_CAP_MATCH_ID(has_sve_feature, ID_AA64ZFR0_EL1, BitPerm, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEBITPERM),
+	HWCAP_CAP_MATCH_ID(has_sve_feature, ID_AA64ZFR0_EL1, B16B16, IMP, CAP_HWCAP, KERNEL_HWCAP_SVE_B16B16),
+	HWCAP_CAP_MATCH_ID(has_sve_feature, ID_AA64ZFR0_EL1, BF16, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEBF16),
+	HWCAP_CAP_MATCH_ID(has_sve_feature, ID_AA64ZFR0_EL1, BF16, EBF16, CAP_HWCAP, KERNEL_HWCAP_SVE_EBF16),
+	HWCAP_CAP_MATCH_ID(has_sve_feature, ID_AA64ZFR0_EL1, SHA3, IMP, CAP_HWCAP, KERNEL_HWCAP_SVESHA3),
+	HWCAP_CAP_MATCH_ID(has_sve_feature, ID_AA64ZFR0_EL1, SM4, IMP, CAP_HWCAP, KERNEL_HWCAP_SVESM4),
+	HWCAP_CAP_MATCH_ID(has_sve_feature, ID_AA64ZFR0_EL1, I8MM, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEI8MM),
+	HWCAP_CAP_MATCH_ID(has_sve_feature, ID_AA64ZFR0_EL1, F32MM, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEF32MM),
+	HWCAP_CAP_MATCH_ID(has_sve_feature, ID_AA64ZFR0_EL1, F64MM, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEF64MM),
 #endif
 #ifdef CONFIG_ARM64_GCS
 	HWCAP_CAP(ID_AA64PFR1_EL1, GCS, IMP, CAP_HWCAP, KERNEL_HWCAP_GCS),