On Tue, Oct 10, 2023 at 10:19:38AM +0200, Borislav Petkov wrote: > On Tue, Oct 10, 2023 at 08:37:16AM +0300, Kirill A. Shutemov wrote: > > On machines with 5-level paging, cpu_feature_enabled(X86_FEATURE_LA57) > > got patched. It includes KASAN code, where KASAN_SHADOW_START depends on > > __VIRTUAL_MASK_SHIFT, which is defined with the cpu_feature_enabled(). > > So use boot_cpu_has(X86_FEATURE_LA57). __VIRTUAL_MASK_SHIFT used in many places. I don't think it is good idea to give up on patching completely. > > It seems that KASAN gets confused when apply_alternatives() patches the > > It seems? Admittedly, I don't understand KASAN well enough. I confirmed my idea indirectly, by patching KASASN_SHADOW_START, as I mentioned. > > KASAN_SHADOW_START users. A test patch that makes KASAN_SHADOW_START > > static, by replacing __VIRTUAL_MASK_SHIFT with 56, fixes the issue. > > > > During text_poke_early() in apply_alternatives(), KASAN should be > > disabled. KASAN is already disabled in non-_early() text_poke(). > > > > It is unclear why the issue was not reported earlier. Bisecting does not > > help. Older kernels trigger the issue less frequently, but it still > > occurs. In the absence of any other clear offenders, the initial dynamic > > 5-level paging support is to blame. > > This whole thing sounds like it is still not really clear what is > actually happening... Maybe KASAN folks can help to understand the situation. -- Kiryl Shutsemau / Kirill A. Shutemov
