From ee017ee353506fcec58e481673e4331ff198a80e Mon Sep 17 00:00:00 2001 From: Jianyong Wu Date: Tue, 1 Feb 2022 19:44:00 +0800 Subject: arm64/mm: avoid fixmap race condition when create pud mapping 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 Reviewed-by: Catalin Marinas 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 --- arch/arm64/mm/mmu.c | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'arch/arm64/mm/mmu.c') 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, -- cgit v1.2.3-59-g8ed1b From 1310222c276b7946e440a7ab49c1e1508561f5fd Mon Sep 17 00:00:00 2001 From: Anshuman Khandual Date: Wed, 16 Feb 2022 10:36:52 +0530 Subject: arm64/mm: Drop use_1G_block() pud_sect_supported() already checks for PUD level block mapping support i.e on ARM64_4K_PAGES config. Hence pud_sect_supported(), along with some other required alignment checks can help completely drop use_1G_block(). Cc: Catalin Marinas Cc: Will Deacon Cc: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Anshuman Khandual Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/1644988012-25455-1-git-send-email-anshuman.khandual@arm.com Signed-off-by: Will Deacon --- arch/arm64/mm/mmu.c | 15 ++------------- 1 file changed, 2 insertions(+), 13 deletions(-) (limited to 'arch/arm64/mm/mmu.c') diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 1681430ecab7..12feac701d8e 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -295,18 +295,6 @@ static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr, } while (addr = next, addr != end); } -static inline bool use_1G_block(unsigned long addr, unsigned long next, - unsigned long phys) -{ - if (PAGE_SHIFT != 12) - return false; - - if (((addr | next | phys) & ~PUD_MASK) != 0) - return false; - - return true; -} - static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end, phys_addr_t phys, pgprot_t prot, phys_addr_t (*pgtable_alloc)(int), @@ -345,7 +333,8 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end, /* * For 4K granule only, attempt to put down a 1GB block */ - if (use_1G_block(addr, next, phys) && + if (pud_sect_supported() && + ((addr | next | phys) & ~PUD_MASK) == 0 && (flags & NO_BLOCK_MAPPINGS) == 0) { pud_set_huge(pudp, phys, prot); -- cgit v1.2.3-59-g8ed1b