Re: [PATCH v11 03/40] arm64: cpufeature: Always specify and use a field width for capabilities

[Qian Cai <quic_qiancai@quicinc.com>]

On Mon, Feb 07, 2022 at 03:20:32PM +0000, Mark Brown wrote:
> Since all the fields in the main ID registers are 4 bits wide we have up
> until now not bothered specifying the width in the code. Since we now
> wish to use this mechanism to enumerate features from the floating point
> feature registers which do not follow this pattern add a width to the
> table.  This means updating all the existing table entries but makes it
> less likely that we run into issues in future due to implicitly assuming
> a 4 bit width.
> 
> Signed-off-by: Mark Brown <broonie@kernel.org>

Do we leave this one alone on purpose?

                .desc = "GIC system register CPU interface",
                .capability = ARM64_HAS_SYSREG_GIC_CPUIF,
                .type = ARM64_CPUCAP_STRICT_BOOT_CPU_FEATURE,
                .matches = has_useable_gicv3_cpuif,
                .sys_reg = SYS_ID_AA64PFR0_EL1,
                .field_pos = ID_AA64PFR0_GIC_SHIFT,
                .sign = FTR_UNSIGNED,
                .min_field_value = 1,

Since width == 0, it will generate an undefined behavior.

UBSAN: shift-out-of-bounds in ./arch/arm64/include/asm/cpufeature.h:535:49
 shift exponent 64 is too large for 64-bit type 'long long unsigned int'
 CPU: 0 PID: 0 Comm: swapper Not tainted 5.17.0-rc6-next-20220301 #1
 Call trace:
  dump_backtrace
  show_stack
  dump_stack_lvl
  dump_stack
  ubsan_epilogue
  __ubsan_handle_shift_out_of_bounds
  has_cpuid_feature
  cpuid_feature_extract_unsigned_field_width at arch/arm64/include/asm/cpufeature.h:535
  (inlined by) cpuid_feature_extract_field_width at arch/arm64/include/asm/cpufeature.h:582
  (inlined by) cpuid_feature_extract_field_width at arch/arm64/include/asm/cpufeature.h:578
  (inlined by) feature_matches at arch/arm64/kernel/cpufeature.c:1317
  (inlined by) has_cpuid_feature at arch/arm64/kernel/cpufeature.c:1335
  has_useable_gicv3_cpuif
  has_useable_gicv3_cpuif at arch/arm64/kernel/cpufeature.c:1389
  update_cpu_capabilities
  init_cpu_features
  cpuinfo_store_boot_cpu
  smp_prepare_boot_cpu
  start_kernel
  __primary_switched