Messages in this thread Patch in this message | | | From | Jianyong Wu <> | Subject | [PATCH v3] arm64/mm: avoid fixmap race condition when create pud mapping | Date | Thu, 16 Dec 2021 16:28:12 +0800 |
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The 'fixmap' is a global resource and is used recursively by create pud mapping(), leading to a potential race condition in the presence of a concurrent call to alloc_init_pud():
kernel_init thread virtio-mem workqueue thread ================== ===========================
alloc_init_pud(...) alloc_init_pud(...) pudp = pud_set_fixmap_offset(...) pudp = pud_set_fixmap_offset(...) READ_ONCE(*pudp) pud_clear_fixmap(...) READ_ONCE(*pudp) // CRASH!
As kernel may sleep during creating pud mapping, introduce a mutex lock to serialise use of the fixmap entries by alloc_init_pud().
Signed-off-by: Jianyong Wu <jianyong.wu@arm.com> ---
Change log:
from v2 to v3: change spin lock to mutex lock as kernel may sleep when create pud map.
arch/arm64/mm/mmu.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index acfae9b41cc8..e680a6a8ca40 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -63,6 +63,7 @@ static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss __maybe_unused; static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss __maybe_unused; static DEFINE_SPINLOCK(swapper_pgdir_lock); +static DEFINE_MUTEX(fixmap_lock); void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd) { @@ -329,6 +330,11 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end, } BUG_ON(p4d_bad(p4d)); + /* + * We only have one fixmap entry per page-table level, so take + * the fixmap lock until we're done. + */ + mutex_lock(&fixmap_lock); pudp = pud_set_fixmap_offset(p4dp, addr); do { pud_t old_pud = READ_ONCE(*pudp); @@ -359,6 +365,7 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end, } while (pudp++, addr = next, addr != end); pud_clear_fixmap(); + mutex_unlock(&fixmap_lock); } static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys, -- 2.17.1
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