Commit a99e07ee authored by Max Filippov's avatar Max Filippov Committed by Chris Zankel

xtensa: check TLB sanity on return to userspace

- check that user TLB mappings correspond to the current page table;
- check that TLB mapping VPN is in the kernel/user address range
  in accordance with its ASID.
Signed-off-by: default avatarMax Filippov <jcmvbkbc@gmail.com>
Signed-off-by: default avatarChris Zankel <chris@zankel.net>
parent c5a771d0
......@@ -2,6 +2,16 @@ menu "Kernel hacking"
source "lib/Kconfig.debug"
config DEBUG_TLB_SANITY
bool "Debug TLB sanity"
depends on DEBUG_KERNEL
help
Enable this to turn on TLB sanity check on each entry to userspace.
This check can spot missing TLB invalidation/wrong PTE permissions/
premature page freeing.
If unsure, say N.
config LD_NO_RELAX
bool "Disable linker relaxation"
default n
......
......@@ -458,7 +458,7 @@ common_exception_return:
_bbsi.l a4, TIF_NEED_RESCHED, 3f
_bbsi.l a4, TIF_NOTIFY_RESUME, 2f
_bbci.l a4, TIF_SIGPENDING, 4f
_bbci.l a4, TIF_SIGPENDING, 5f
2: l32i a4, a1, PT_DEPC
bgeui a4, VALID_DOUBLE_EXCEPTION_ADDRESS, 4f
......@@ -476,6 +476,13 @@ common_exception_return:
callx4 a4
j 1b
5:
#ifdef CONFIG_DEBUG_TLB_SANITY
l32i a4, a1, PT_DEPC
bgeui a4, VALID_DOUBLE_EXCEPTION_ADDRESS, 4f
movi a4, check_tlb_sanity
callx4 a4
#endif
4: /* Restore optional registers. */
load_xtregs_opt a1 a2 a4 a5 a6 a7 PT_XTREGS_OPT
......
......@@ -141,3 +141,116 @@ void flush_tlb_page (struct vm_area_struct *vma, unsigned long page)
local_irq_restore(flags);
}
#ifdef CONFIG_DEBUG_TLB_SANITY
static unsigned get_pte_for_vaddr(unsigned vaddr)
{
struct task_struct *task = get_current();
struct mm_struct *mm = task->mm;
pgd_t *pgd;
pmd_t *pmd;
pte_t *pte;
if (!mm)
mm = task->active_mm;
pgd = pgd_offset(mm, vaddr);
if (pgd_none_or_clear_bad(pgd))
return 0;
pmd = pmd_offset(pgd, vaddr);
if (pmd_none_or_clear_bad(pmd))
return 0;
pte = pte_offset_map(pmd, vaddr);
if (!pte)
return 0;
return pte_val(*pte);
}
enum {
TLB_SUSPICIOUS = 1,
TLB_INSANE = 2,
};
static void tlb_insane(void)
{
BUG_ON(1);
}
static void tlb_suspicious(void)
{
WARN_ON(1);
}
/*
* Check that TLB entries with kernel ASID (1) have kernel VMA (>= TASK_SIZE),
* and TLB entries with user ASID (>=4) have VMA < TASK_SIZE.
*
* Check that valid TLB entries either have the same PA as the PTE, or PTE is
* marked as non-present. Non-present PTE and the page with non-zero refcount
* and zero mapcount is normal for batched TLB flush operation. Zero refcount
* means that the page was freed prematurely. Non-zero mapcount is unusual,
* but does not necessary means an error, thus marked as suspicious.
*/
static int check_tlb_entry(unsigned w, unsigned e, bool dtlb)
{
unsigned tlbidx = w | (e << PAGE_SHIFT);
unsigned r0 = dtlb ?
read_dtlb_virtual(tlbidx) : read_itlb_virtual(tlbidx);
unsigned vpn = (r0 & PAGE_MASK) | (e << PAGE_SHIFT);
unsigned pte = get_pte_for_vaddr(vpn);
unsigned mm_asid = (get_rasid_register() >> 8) & ASID_MASK;
unsigned tlb_asid = r0 & ASID_MASK;
bool kernel = tlb_asid == 1;
int rc = 0;
if (tlb_asid > 0 && ((vpn < TASK_SIZE) == kernel)) {
pr_err("%cTLB: way: %u, entry: %u, VPN %08x in %s PTE\n",
dtlb ? 'D' : 'I', w, e, vpn,
kernel ? "kernel" : "user");
rc |= TLB_INSANE;
}
if (tlb_asid == mm_asid) {
unsigned r1 = dtlb ? read_dtlb_translation(tlbidx) :
read_itlb_translation(tlbidx);
if ((pte ^ r1) & PAGE_MASK) {
pr_err("%cTLB: way: %u, entry: %u, mapping: %08x->%08x, PTE: %08x\n",
dtlb ? 'D' : 'I', w, e, r0, r1, pte);
if (pte == 0 || !pte_present(__pte(pte))) {
struct page *p = pfn_to_page(r1 >> PAGE_SHIFT);
pr_err("page refcount: %d, mapcount: %d\n",
page_count(p),
page_mapcount(p));
if (!page_count(p))
rc |= TLB_INSANE;
else if (page_mapped(p))
rc |= TLB_SUSPICIOUS;
} else {
rc |= TLB_INSANE;
}
}
}
return rc;
}
void check_tlb_sanity(void)
{
unsigned long flags;
unsigned w, e;
int bug = 0;
local_irq_save(flags);
for (w = 0; w < DTLB_ARF_WAYS; ++w)
for (e = 0; e < (1 << XCHAL_DTLB_ARF_ENTRIES_LOG2); ++e)
bug |= check_tlb_entry(w, e, true);
for (w = 0; w < ITLB_ARF_WAYS; ++w)
for (e = 0; e < (1 << XCHAL_ITLB_ARF_ENTRIES_LOG2); ++e)
bug |= check_tlb_entry(w, e, false);
if (bug & TLB_INSANE)
tlb_insane();
if (bug & TLB_SUSPICIOUS)
tlb_suspicious();
local_irq_restore(flags);
}
#endif /* CONFIG_DEBUG_TLB_SANITY */
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