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SubjectRe: [PATCH 1/2] x86: mm: ptdump: Calculate effective permissions correctly
On Thu, May 21, 2020 at 04:23:07PM +0100, Steven Price wrote:
> --- a/arch/x86/mm/dump_pagetables.c
> +++ b/arch/x86/mm/dump_pagetables.c
> @@ -249,10 +249,22 @@ static void note_wx(struct pg_state *st, unsigned long addr)
> @@ -270,16 +282,10 @@ static void note_page(struct ptdump_state *pt_st, unsigned long addr, int level,
> struct seq_file *m = st->seq;
>
> new_prot = val & PTE_FLAGS_MASK;
> + new_eff = st->prot_levels[level];

This will trigger,

.config (if ever matters):
https://raw.githubusercontent.com/cailca/linux-mm/master/x86.config

[ 104.532621] UBSAN: array-index-out-of-bounds in arch/x86/mm/dump_pagetables.c:284:27
[ 104.542620] index -1 is out of range for type 'pgprotval_t [5]'
[ 104.552624] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.7.0-rc6-next-20200522+ #5
[ 104.560865] Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
[ 104.562604] Call Trace:
[ 104.562604] dump_stack+0xa7/0xea
[ 104.562604] ubsan_epilogue+0x9/0x45
[ 104.562604] __ubsan_handle_out_of_bounds.cold.12+0x2b/0x36
[ 104.562604] ? __kasan_check_write+0x14/0x20
[ 104.562604] note_page+0x91f/0xa00
[ 104.562604] ? down_read_non_owner+0x330/0x330
[ 104.562604] ? match_held_lock+0x20/0x250
[ 104.562604] ptdump_walk_pgd+0xa1/0xb0
[ 104.562604] ptdump_walk_pgd_level_core+0x19f/0x200
[ 104.562604] ? up+0x46/0x60
[ 104.562604] ? hugetlb_get_unmapped_area+0x590/0x590
[ 104.562604] ? lock_downgrade+0x3e0/0x3e0
[ 104.562604] ? _raw_spin_unlock_irqrestore+0x44/0x50
[ 104.562604] ? ptdump_walk_pgd_level_debugfs+0x80/0x80
[ 104.562604] ? ptdump_walk_pgd_level_core+0x200/0x200
[ 104.562604] ? virt_efi_set_variable_nonblocking+0xf1/0x110
[ 104.562604] ptdump_walk_pgd_level+0x32/0x40
[ 104.562604] efi_dump_pagetable+0x17/0x19
[ 104.562604] efi_enter_virtual_mode+0x3e5/0x3f5
[ 104.562604] start_kernel+0x848/0x8f6
[ 104.562604] ? __early_make_pgtable+0x2cb/0x314
[ 104.562604] ? thread_stack_cache_init+0xb/0xb
[ 104.562604] ? early_make_pgtable+0x21/0x23
[ 104.562604] ? early_idt_handler_common+0x35/0x4c
[ 104.562604] x86_64_start_reservations+0x24/0x26
[ 104.562604] x86_64_start_kernel+0xf4/0xfb
[ 104.562604] secondary_startup_64+0xb6/0xc0

>
> - if (level > 0) {
> - new_eff = effective_prot(st->prot_levels[level - 1],
> - new_prot);
> - } else {
> - new_eff = new_prot;
> - }
> -
> - if (level >= 0)
> - st->prot_levels[level] = new_eff;
> + if (!val)
> + new_eff = 0;
>
> /*
> * If we have a "break" in the series, we need to flush the state that

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