x86/cpu: Don't transiently clear the boot CPU's capabilities

On the boot CPU, identify_cpu() runs from arch_cpu_finalize_init(), with
interrupts enabled and before alternatives are patched. So
cpu_feature_enabled() still evaluates against boot_cpu_data.

identify_cpu() rebuilds c->x86_capability from scratch: the reset zeroes the
array and the CPUID rescan fills it in again. An interrupt delivered in that
window finds X86_FEATURE_LA57 clear in boot_cpu_data, so pgtable_l5_enabled()
is false and KASAN checks a 5-level address against the 4-level addressability
limit. The result is a bogus "wild-memory-access" report, and under
kasan_multi_shot a report storm that wedges the boot.

The boot CPU has already been scanned by early_identify_cpu(), with interrupts
disabled, and its capabilities cannot have changed since. Reset only the CPUs
which have not been scanned yet.

The window is as old as identify_cpu() rebuilding the capabilities.  Commit

  39b9552281ab ("x86/mm: Optimize boot-time paging mode switching cost")

merely let KASAN notice it by making pgtable_l5_enabled() read the feature
bit. So no Fixes: tag.

Closes: https://lore.kernel.org/bpf/20260610175651.647515-1-ihor.solodrai@linux.dev/
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/20260916195203.1099646-6-ihor.solodrai@linux.dev

0 files changed, 0 insertions, 0 deletions