On Tue, Jan 07, 2025 at 10:59:41PM +0000, Mark Brown wrote:
From: Marc Zyngier maz@kernel.org
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: Catalin Marinas catalin.marinas@arm.com