> /* > + * Find virtual (VA) and physical (PA) addresses of kernel start > + * > + * va: > + * Actual address of the kernel start (_stext) placed > + * randomly by kaslr feature. To be more accurate, > + * VA = _stext(from vmlinux) + kaslr_offset > + * > + * pa: > + * Physical address where the kerenel is placed. > + * > + * In nokaslr case, VA = _stext (from vmlinux) > + * In kaslr case, virtual address of the kernel placement goes > + * in this range: ffffffff80000000..ffffffff9fffffff, or > + * __START_KERNEL_map..+512MB > + * > + * https://www.kernel.org/doc/Documentation/x86/x86_64/mm.txt > + * > + * Randomized VA will be the first valid page starting from > + * ffffffff80000000 (__START_KERNEL_map). Page tree entry of > + * this page will contain the PA of the kernel start. I didn't come up with this natural idea, which is better in that IDTR is unnecessary. > + * > + * NOTES: > + * 1. This method does not support PTI (Page Table Isolation) > + * case where CR3 points to the isolated page tree. calc_kaslr_offset() already deals with PTI here: if (st->pti_init_vmlinux || st->kaiser_init_vmlinux) pgd = cr3 & ~(CR3_PCID_MASK|PTI_USER_PGTABLE_MASK); else pgd = cr3 & ~CR3_PCID_MASK; Thus it's OK to think that the CR3 points at the kernel counterpart. > + * 2. 4-level paging support only, as caller (calc_kaslr_offset) > + * does not support 5-level paging. According to the mm.txt the address range for kernel text appears same in 5-level paging. What is the reason not to cover 5-level paging in this patch? Is there something that cannot be assumed on 5-level paging? > + */ > +static int > +find_kernel_start(ulong *va, ulong *pa) > +{ > + int i, pgd_idx, pud_idx, pmd_idx, pte_idx; > + uint64_t pgd_pte, pud_pte, pmd_pte, pte; > + > + pgd_idx = pgd_index(__START_KERNEL_map); > + pud_idx = pud_index(__START_KERNEL_map); > + pmd_idx = pmd_index(__START_KERNEL_map); > + pte_idx = pte_index(__START_KERNEL_map); > + > + for (; pgd_idx < PTRS_PER_PGD; pgd_idx++) { > + pgd_pte = ULONG(machdep->pgd + pgd_idx * sizeof(uint64_t)); machdep->pgd is not guaranteed to be aligned by PAGE_SIZE. This could refer to the pgd for userland that resides in the next page. I guess it's necessary to get the 1st pgd entry in the page machdep->pgd belongs to. Like this? pgd_pte = ULONG((machdep->pgd & PHYSICAL_PAGE_MASK) + pgd_idx * sizeof(uint64_t)); Thanks. HATAYAMA, Daisuke -- Crash-utility mailing list Crash-utility@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/crash-utility
