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Date: Mon, 24 Jan 2022 18:47:43 +0100 From: Ard Biesheuvel <ardb@...nel.org> To: linux@...linux.org.uk, linux-arm-kernel@...ts.infradead.org Cc: linux-hardening@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>, Nicolas Pitre <nico@...xnic.net>, Arnd Bergmann <arnd@...db.de>, Kees Cook <keescook@...omium.org>, Keith Packard <keithpac@...zon.com>, Linus Walleij <linus.walleij@...aro.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Tony Lindgren <tony@...mide.com>, Marc Zyngier <maz@...nel.org>, Vladimir Murzin <vladimir.murzin@....com>, Jesse Taube <mr.bossman075@...il.com> Subject: [PATCH v5 31/32] ARM: mm: prepare vmalloc_seq handling for use under SMP Currently, the vmalloc_seq counter is only used to keep track of changes in the vmalloc region on !SMP builds, which means there is no need to deal with concurrency explicitly. However, in a subsequent patch, we will wire up this same mechanism for ensuring that vmap'ed stacks are guaranteed to be mapped by the active mm before switching to a task, and here we need to ensure that changes to the page tables are visible to other CPUs when they observe a change in the sequence count. Since LPAE needs none of this, fold a check against it into the vmalloc_seq counter check after breaking it out into a separate static inline helper. Signed-off-by: Ard Biesheuvel <ardb@...nel.org> --- arch/arm/include/asm/mmu.h | 2 +- arch/arm/include/asm/mmu_context.h | 13 +++++++++++-- arch/arm/mm/context.c | 3 +-- arch/arm/mm/ioremap.c | 18 +++++++++++------- 4 files changed, 24 insertions(+), 12 deletions(-) diff --git a/arch/arm/include/asm/mmu.h b/arch/arm/include/asm/mmu.h index 1592a4264488..e049723840d3 100644 --- a/arch/arm/include/asm/mmu.h +++ b/arch/arm/include/asm/mmu.h @@ -10,7 +10,7 @@ typedef struct { #else int switch_pending; #endif - unsigned int vmalloc_seq; + atomic_t vmalloc_seq; unsigned long sigpage; #ifdef CONFIG_VDSO unsigned long vdso; diff --git a/arch/arm/include/asm/mmu_context.h b/arch/arm/include/asm/mmu_context.h index 84e58956fcab..71a26986efb9 100644 --- a/arch/arm/include/asm/mmu_context.h +++ b/arch/arm/include/asm/mmu_context.h @@ -23,6 +23,16 @@ void __check_vmalloc_seq(struct mm_struct *mm); +#ifdef CONFIG_MMU +static inline void check_vmalloc_seq(struct mm_struct *mm) +{ + if (!IS_ENABLED(CONFIG_ARM_LPAE) && + unlikely(atomic_read(&mm->context.vmalloc_seq) != + atomic_read(&init_mm.context.vmalloc_seq))) + __check_vmalloc_seq(mm); +} +#endif + #ifdef CONFIG_CPU_HAS_ASID void check_and_switch_context(struct mm_struct *mm, struct task_struct *tsk); @@ -52,8 +62,7 @@ static inline void a15_erratum_get_cpumask(int this_cpu, struct mm_struct *mm, static inline void check_and_switch_context(struct mm_struct *mm, struct task_struct *tsk) { - if (unlikely(mm->context.vmalloc_seq != init_mm.context.vmalloc_seq)) - __check_vmalloc_seq(mm); + check_vmalloc_seq(mm); if (irqs_disabled()) /* diff --git a/arch/arm/mm/context.c b/arch/arm/mm/context.c index 48091870db89..4204ffa2d104 100644 --- a/arch/arm/mm/context.c +++ b/arch/arm/mm/context.c @@ -240,8 +240,7 @@ void check_and_switch_context(struct mm_struct *mm, struct task_struct *tsk) unsigned int cpu = smp_processor_id(); u64 asid; - if (unlikely(mm->context.vmalloc_seq != init_mm.context.vmalloc_seq)) - __check_vmalloc_seq(mm); + check_vmalloc_seq(mm); /* * We cannot update the pgd and the ASID atomicly with classic diff --git a/arch/arm/mm/ioremap.c b/arch/arm/mm/ioremap.c index 197f8eb3a775..aa08bcb72db9 100644 --- a/arch/arm/mm/ioremap.c +++ b/arch/arm/mm/ioremap.c @@ -117,16 +117,21 @@ EXPORT_SYMBOL(ioremap_page); void __check_vmalloc_seq(struct mm_struct *mm) { - unsigned int seq; + int seq; do { - seq = init_mm.context.vmalloc_seq; + seq = atomic_read(&init_mm.context.vmalloc_seq); memcpy(pgd_offset(mm, VMALLOC_START), pgd_offset_k(VMALLOC_START), sizeof(pgd_t) * (pgd_index(VMALLOC_END) - pgd_index(VMALLOC_START))); - mm->context.vmalloc_seq = seq; - } while (seq != init_mm.context.vmalloc_seq); + /* + * Use a store-release so that other CPUs that observe the + * counter's new value are guaranteed to see the results of the + * memcpy as well. + */ + atomic_set_release(&mm->context.vmalloc_seq, seq); + } while (seq != atomic_read(&init_mm.context.vmalloc_seq)); } #if !defined(CONFIG_SMP) && !defined(CONFIG_ARM_LPAE) @@ -157,7 +162,7 @@ static void unmap_area_sections(unsigned long virt, unsigned long size) * Note: this is still racy on SMP machines. */ pmd_clear(pmdp); - init_mm.context.vmalloc_seq++; + atomic_inc_return_release(&init_mm.context.vmalloc_seq); /* * Free the page table, if there was one. @@ -174,8 +179,7 @@ static void unmap_area_sections(unsigned long virt, unsigned long size) * Ensure that the active_mm is up to date - we want to * catch any use-after-iounmap cases. */ - if (current->active_mm->context.vmalloc_seq != init_mm.context.vmalloc_seq) - __check_vmalloc_seq(current->active_mm); + check_vmalloc_seq(current->active_mm); flush_tlb_kernel_range(virt, end); } -- 2.30.2
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