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arm64/mm: avoid fixmap race condition when create pud mapping
[ Upstream commitee017ee353
] 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:f471044545
("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>
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1 changed files with 9 additions and 0 deletions
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@ -63,6 +63,7 @@ static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss __maybe_unused;
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static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss __maybe_unused;
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static DEFINE_SPINLOCK(swapper_pgdir_lock);
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static DEFINE_MUTEX(fixmap_lock);
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void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd)
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{
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@ -328,6 +329,12 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
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}
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BUG_ON(p4d_bad(p4d));
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/*
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* No need for locking during early boot. And it doesn't work as
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* expected with KASLR enabled.
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*/
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if (system_state != SYSTEM_BOOTING)
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mutex_lock(&fixmap_lock);
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pudp = pud_set_fixmap_offset(p4dp, addr);
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do {
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pud_t old_pud = READ_ONCE(*pudp);
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@ -358,6 +365,8 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
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} while (pudp++, addr = next, addr != end);
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pud_clear_fixmap();
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if (system_state != SYSTEM_BOOTING)
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mutex_unlock(&fixmap_lock);
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}
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static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys,
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