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

commit 064737920bdbca86df91b96aed256e88018fef3a upstream.

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>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: stable@vger.kernel.org
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250107-arm64-2024-dpisa-v5-1-7578da51fc3d@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 26 insertions, 13 deletions

diff --git a/Documentation/arch/arm64/elf_hwcaps.rst b/Documentation/arch/arm64/elf_hwcaps.rst
index 2ff922a406ad..1a31723e79fd 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.