From: Steven Price steven.price@arm.com Subject: x86: mm: ptdump: calculate effective permissions correctly

Patch series "Fix W+X debug feature on x86"

Jan alerted me[1] that the W+X detection debug feature was broken in x86 by my change[2] to switch x86 to use the generic ptdump infrastructure.

Fundamentally the approach of trying to move the calculation of effective permissions into note_page() was broken because note_page() is only called for 'leaf' entries and the effective permissions are passed down via the internal nodes of the page tree. The solution I've taken here is to create a new (optional) callback which is called for all nodes of the page tree and therefore can calculate the effective permissions.

Secondly on some configurations (32 bit with PAE) "unsigned long" is not large enough to store the table entries. The fix here is simple - let's just use a u64.

[1] https://lore.kernel.org/lkml/d573dc7e-e742-84de-473d-f971142fa319@suse.com/ [2] 2ae27137b2db ("x86: mm: convert dump_pagetables to use walk_page_range")

This patch (of 2):

By switching the x86 page table dump code to use the generic code the effective permissions are no longer calculated correctly because the note_page() function is only called for *leaf* entries. To calculate the actual effective permissions it is necessary to observe the full hierarchy of the page tree.

Introduce a new callback for ptdump which is called for every entry and can therefore update the prot_levels array correctly. note_page() can then simply access the appropriate element in the array.

[steven.price@arm.com: make the assignment conditional on val != 0] Link: http://lkml.kernel.org/r/430c8ab4-e7cd-6933-dde6-087fac6db872@arm.com Link: http://lkml.kernel.org/r/20200521152308.33096-1-steven.price@arm.com Link: http://lkml.kernel.org/r/20200521152308.33096-2-steven.price@arm.com Fixes: 2ae27137b2db ("x86: mm: convert dump_pagetables to use walk_page_range") Signed-off-by: Steven Price steven.price@arm.com Reported-by: Jan Beulich jbeulich@suse.com Cc: Qian Cai cai@lca.pw Cc: Andy Lutomirski luto@kernel.org Cc: Borislav Petkov bp@alien8.de Cc: Dave Hansen dave.hansen@linux.intel.com Cc: Ingo Molnar mingo@redhat.com Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

arch/x86/mm/dump_pagetables.c | 33 +++++++++++++++++++------------- include/linux/ptdump.h | 1 mm/ptdump.c | 17 +++++++++++++++- 3 files changed, 37 insertions(+), 14 deletions(-)

--- a/arch/x86/mm/dump_pagetables.c~x86-mm-ptdump-calculate-effective-permissions-correctly +++ a/arch/x86/mm/dump_pagetables.c @@ -249,10 +249,22 @@ static void note_wx(struct pg_state *st, (void *)st->start_address); }

-static inline pgprotval_t effective_prot(pgprotval_t prot1, pgprotval_t prot2) +static void effective_prot(struct ptdump_state *pt_st, int level, u64 val) { - return (prot1 & prot2 & (_PAGE_USER | _PAGE_RW)) | - ((prot1 | prot2) & _PAGE_NX); + struct pg_state *st = container_of(pt_st, struct pg_state, ptdump); + pgprotval_t prot = val & PTE_FLAGS_MASK; + pgprotval_t effective; + + if (level > 0) { + pgprotval_t higher_prot = st->prot_levels[level - 1]; + + effective = (higher_prot & prot & (_PAGE_USER | _PAGE_RW)) | + ((higher_prot | prot) & _PAGE_NX); + } else { + effective = prot; + } + + st->prot_levels[level] = effective; }

/* @@ -270,16 +282,10 @@ static void note_page(struct ptdump_stat struct seq_file *m = st->seq;

new_prot = val & PTE_FLAGS_MASK; - - 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; + else + new_eff = st->prot_levels[level];

/* * If we have a "break" in the series, we need to flush the state that @@ -374,6 +380,7 @@ static void ptdump_walk_pgd_level_core(s struct pg_state st = { .ptdump = { .note_page = note_page, + .effective_prot = effective_prot, .range = ptdump_ranges }, .level = -1, --- a/include/linux/ptdump.h~x86-mm-ptdump-calculate-effective-permissions-correctly +++ a/include/linux/ptdump.h @@ -14,6 +14,7 @@ struct ptdump_state { /* level is 0:PGD to 4:PTE, or -1 if unknown */ void (*note_page)(struct ptdump_state *st, unsigned long addr, int level, unsigned long val); + void (*effective_prot)(struct ptdump_state *st, int level, u64 val); const struct ptdump_range *range; };

--- a/mm/ptdump.c~x86-mm-ptdump-calculate-effective-permissions-correctly +++ a/mm/ptdump.c @@ -36,6 +36,9 @@ static int ptdump_pgd_entry(pgd_t *pgd, return note_kasan_page_table(walk, addr); #endif

+ if (st->effective_prot) + st->effective_prot(st, 0, pgd_val(val)); + if (pgd_leaf(val)) st->note_page(st, addr, 0, pgd_val(val));

@@ -53,6 +56,9 @@ static int ptdump_p4d_entry(p4d_t *p4d, return note_kasan_page_table(walk, addr); #endif

+ if (st->effective_prot) + st->effective_prot(st, 1, p4d_val(val)); + if (p4d_leaf(val)) st->note_page(st, addr, 1, p4d_val(val));

@@ -70,6 +76,9 @@ static int ptdump_pud_entry(pud_t *pud, return note_kasan_page_table(walk, addr); #endif

+ if (st->effective_prot) + st->effective_prot(st, 2, pud_val(val)); + if (pud_leaf(val)) st->note_page(st, addr, 2, pud_val(val));

@@ -87,6 +96,8 @@ static int ptdump_pmd_entry(pmd_t *pmd, return note_kasan_page_table(walk, addr); #endif

+ if (st->effective_prot) + st->effective_prot(st, 3, pmd_val(val)); if (pmd_leaf(val)) st->note_page(st, addr, 3, pmd_val(val));

@@ -97,8 +108,12 @@ static int ptdump_pte_entry(pte_t *pte, unsigned long next, struct mm_walk *walk) { struct ptdump_state *st = walk->private; + pte_t val = READ_ONCE(*pte); + + if (st->effective_prot) + st->effective_prot(st, 4, pte_val(val));

- st->note_page(st, addr, 4, pte_val(READ_ONCE(*pte))); + st->note_page(st, addr, 4, pte_val(val));

return 0; } _