From ee017ee353506fcec58e481673e4331ff198a80e Mon Sep 17 00:00:00 2001
From: Jianyong Wu <jianyong.wu@arm.com>
Date: Tue, 1 Feb 2022 19:44:00 +0800
Subject: [PATCH] arm64/mm: avoid fixmap race condition when create pud mapping
Git-commit: ee017ee353506fcec58e481673e4331ff198a80e
Patch-mainline: v5.18-rc1
References: git-fixes
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>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
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 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,
--
2.31.1