From: Jianyong Wu jianyong.wu@arm.com
[ Upstream commit ee017ee353506fcec58e481673e4331ff198a80e ]
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 Reviewed-by: Catalin Marinas catalin.marinas@arm.com Fixes: f4710445458c ("arm64: mm: use fixmap when creating page tables") Link: https://lore.kernel.org/r/20220201114400.56885-1-jianyong.wu@arm.com Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm64/mm/mmu.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 9d0380631690..03aa6bee7dae 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) { @@ -328,6 +329,12 @@ 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); @@ -358,6 +365,8 @@ 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,