| Message ID | 20220201114400.56885-1-jianyong.wu@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v4] arm64/mm: avoid fixmap race condition when create pud mapping | expand |
On Tue, Feb 01, 2022 at 07:44:00PM +0800, Jianyong Wu wrote: > 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(). However, there is > no need for locking in early boot stage and it doesn't work well with > KASLR enabled when early boot. So, enable lock when system_state doesn't > equal to "SYSTEM_BOOTING". > > Signed-off-by: Jianyong Wu <jianyong.wu@arm.com> This looks fine to me but I'd rather leave it in -next for a bit given that we attempted to fix it a couple of times and got it wrong. Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
On Tue, 1 Feb 2022 19:44:00 +0800, Jianyong Wu wrote: > 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 > ================== =========================== > > [...] Applied to arm64 (for-next/mm), thanks! [1/1] arm64/mm: avoid fixmap race condition when create pud mapping https://git.kernel.org/arm64/c/ee017ee35350 Cheers,
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index acfae9b41cc8..1681430ecab7 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 +330,12 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end, } BUG_ON(p4d_bad(p4d)); + /* + * No need for locking during early boot. And it doesn't work as + * expected with KASLR enabled. + */ + if (system_state != SYSTEM_BOOTING) + mutex_lock(&fixmap_lock); pudp = pud_set_fixmap_offset(p4dp, addr); do { pud_t old_pud = READ_ONCE(*pudp); @@ -359,6 +366,8 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end, } while (pudp++, addr = next, addr != end); pud_clear_fixmap(); + if (system_state != SYSTEM_BOOTING) + mutex_unlock(&fixmap_lock); } static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys,
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(). However, there is no need for locking in early boot stage and it doesn't work well with KASLR enabled when early boot. So, enable lock when system_state doesn't equal to "SYSTEM_BOOTING". Signed-off-by: Jianyong Wu <jianyong.wu@arm.com> --- Change log: from v3 to v4: conditionally enable lock as we doesn't need lock when early boot. from v2 to v3: change spin lock to mutex lock as kernel may sleep when create pud map. --- arch/arm64/mm/mmu.c | 9 +++++++++ 1 file changed, 9 insertions(+)