On 11/24/20 15:50, Will Deacon wrote:
> When confronted with a mixture of CPUs, some of which support 32-bit
Confronted made me laugh, well chosen word! :D
For some reason made me think of this :p
https://www.youtube.com/watch?v=NJbXPzSPzxc&t=1m33s
> applications and others which don't, we quite sensibly treat the system
> as 64-bit only for userspace and prevent execve() of 32-bit binaries.
>
> Unfortunately, some crazy folks have decided to build systems like this
> with the intention of running 32-bit applications, so relax our
> sanitisation logic to continue to advertise 32-bit support to userspace
> on these systems and track the real 32-bit capable cores in a cpumask
> instead. For now, the default behaviour remains but will be tied to
> a command-line option in a later patch.
>
> Signed-off-by: Will Deacon <w...@kernel.org>
> ---
> arch/arm64/include/asm/cpucaps.h | 2 +-
> arch/arm64/include/asm/cpufeature.h | 8 ++-
> arch/arm64/kernel/cpufeature.c | 106 ++++++++++++++++++++++++++--
> 3 files changed, 107 insertions(+), 9 deletions(-)
>
> diff --git a/arch/arm64/include/asm/cpucaps.h
> b/arch/arm64/include/asm/cpucaps.h
> index e7d98997c09c..e6f0eb4643a0 100644
> --- a/arch/arm64/include/asm/cpucaps.h
> +++ b/arch/arm64/include/asm/cpucaps.h
> @@ -20,7 +20,7 @@
> #define ARM64_ALT_PAN_NOT_UAO 10
> #define ARM64_HAS_VIRT_HOST_EXTN 11
> #define ARM64_WORKAROUND_CAVIUM_27456 12
> -#define ARM64_HAS_32BIT_EL0 13
> +#define ARM64_HAS_32BIT_EL0_DO_NOT_USE 13
nit: would UNUSED be better here? Worth adding a comment as to why too?
> #define ARM64_HARDEN_EL2_VECTORS 14
> #define ARM64_HAS_CNP 15
> #define ARM64_HAS_NO_FPSIMD 16
[...]
> +static bool has_32bit_el0(const struct arm64_cpu_capabilities *entry, int
> scope)
> +{
> + if (!has_cpuid_feature(entry, scope))
> + return allow_mismatched_32bit_el0;
If a user passes the command line by mistake on a 64bit only system, this will
return true. I'll be honest, I'm not entirely sure what the impact is. I get
lost in the features maze. It is nicely encapsulated, but hard to navigate for
the none initiated :-)
Thanks
--
Qais Yousef
> +
> + if (scope == SCOPE_SYSTEM)
> + pr_info("detected: 32-bit EL0 Support\n");
> +
> + return true;
> +}
> +
> static bool has_useable_gicv3_cpuif(const struct arm64_cpu_capabilities
> *entry, int scope)
> {
> bool has_sre;
> @@ -1803,10 +1890,9 @@ static const struct arm64_cpu_capabilities
> arm64_features[] = {
> },
> #endif /* CONFIG_ARM64_VHE */
> {
> - .desc = "32-bit EL0 Support",
> - .capability = ARM64_HAS_32BIT_EL0,
> + .capability = ARM64_HAS_32BIT_EL0_DO_NOT_USE,
> .type = ARM64_CPUCAP_SYSTEM_FEATURE,
> - .matches = has_cpuid_feature,
> + .matches = has_32bit_el0,
> .sys_reg = SYS_ID_AA64PFR0_EL1,
> .sign = FTR_UNSIGNED,
> .field_pos = ID_AA64PFR0_EL0_SHIFT,
> @@ -2299,7 +2385,7 @@ static const struct arm64_cpu_capabilities
> compat_elf_hwcaps[] = {
> {},
> };
