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Date: Tue, 6 Oct 2020 17:34:16 +0200 From: David Hildenbrand <david@...hat.com> To: Anshuman Khandual <anshuman.khandual@....com>, linux-arm-kernel@...ts.infradead.org Cc: will@...nel.org, catalin.marinas@....com, Mark Rutland <mark.rutland@....com>, Ard Biesheuvel <ardb@...nel.org>, Steven Price <steven.price@....com>, Robin Murphy <robin.murphy@....com>, Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...nel.org> Subject: Re: [PATCH] arm64/mm: Validate hotplug range before creating linear mapping On 17.09.20 10:46, Anshuman Khandual wrote: > During memory hotplug process, the linear mapping should not be created for > a given memory range if that would fall outside the maximum allowed linear > range. Else it might cause memory corruption in the kernel virtual space. > > Maximum linear mapping region is [PAGE_OFFSET..(PAGE_END -1)] accommodating > both its ends but excluding PAGE_END. Max physical range that can be mapped > inside this linear mapping range, must also be derived from its end points. > > When CONFIG_ARM64_VA_BITS_52 is enabled, PAGE_OFFSET is computed with the > assumption of 52 bits virtual address space. However, if the CPU does not > support 52 bits, then it falls back using 48 bits instead and the PAGE_END > is updated to reflect this using the vabits_actual. As for PAGE_OFFSET, > bits [51..48] are ignored by the MMU and remain unchanged, even though the > effective start address of linear map is now slightly different. Hence, to > reliably check the physical address range mapped by the linear map, the > start address should be calculated using vabits_actual. This ensures that > arch_add_memory() validates memory hot add range for its potential linear > mapping requirement, before creating it with __create_pgd_mapping(). > > Cc: Catalin Marinas <catalin.marinas@....com> > Cc: Will Deacon <will@...nel.org> > Cc: Mark Rutland <mark.rutland@....com> > Cc: Ard Biesheuvel <ardb@...nel.org> > Cc: Steven Price <steven.price@....com> > Cc: Robin Murphy <robin.murphy@....com> > Cc: David Hildenbrand <david@...hat.com> > Cc: Andrew Morton <akpm@...ux-foundation.org> > Cc: linux-arm-kernel@...ts.infradead.org > Cc: linux-kernel@...r.kernel.org > Fixes: 4ab215061554 ("arm64: Add memory hotplug support") > Signed-off-by: Anshuman Khandual <anshuman.khandual@....com> > --- > arch/arm64/mm/mmu.c | 27 +++++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 75df62fea1b6..d59ffabb9c84 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -1433,11 +1433,38 @@ static void __remove_pgd_mapping(pgd_t *pgdir, unsigned long start, u64 size) > free_empty_tables(start, end, PAGE_OFFSET, PAGE_END); > } > > +static bool inside_linear_region(u64 start, u64 size) > +{ > + /* > + * Linear mapping region is the range [PAGE_OFFSET..(PAGE_END - 1)] > + * accommodating both its ends but excluding PAGE_END. Max physical > + * range which can be mapped inside this linear mapping range, must > + * also be derived from its end points. > + * > + * With CONFIG_ARM64_VA_BITS_52 enabled, PAGE_OFFSET is defined with > + * the assumption of 52 bits virtual address space. However, if the > + * CPU does not support 52 bits, it falls back using 48 bits and the > + * PAGE_END is updated to reflect this using the vabits_actual. As > + * for PAGE_OFFSET, bits [51..48] are ignored by the MMU and remain > + * unchanged, even though the effective start address of linear map > + * is now slightly different. Hence, to reliably check the physical > + * address range mapped by the linear map, the start address should > + * be calculated using vabits_actual. > + */ > + return ((start >= __pa(_PAGE_OFFSET(vabits_actual))) > + && ((start + size) <= __pa(PAGE_END - 1))); > +} > + > int arch_add_memory(int nid, u64 start, u64 size, > struct mhp_params *params) > { > int ret, flags = 0; > > + if (!inside_linear_region(start, size)) { > + pr_err("[%llx %llx] is outside linear mapping region\n", start, start + size); > + return -EINVAL; > + } > + > if (rodata_full || debug_pagealloc_enabled()) > flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; > > Can we please provide a generic way to figure limits like that out, especially, before calling add_memory() and friends? We do have __add_pages()->check_hotplug_memory_addressable() where we already check against MAX_PHYSMEM_BITS. What I'd prefer is a way to get 1. Lower address limit we can use for add_memory() and friends 2. Upper address limit we can use for add_memory() and friends something like struct range memhp_get_addressable_range(void) { const u64 max_phys = (1ull << (MAX_PHYSMEM_BITS + 1)) - 1; struct range range = arch_get_mappable_range(); if (range.start > max_phys) { range.start = 0; range.end = 0; } range.end = max_t(u64, range.end, max_phys); return range; } That, we can use in check_hotplug_memory_addressable(), and also allow add_memory*() users to make use of it. -- Thanks, David / dhildenb
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