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MIPS: Bounds check virt_addr_valid
The virt_addr_valid() function is meant to return true iff virt_to_page() will return a valid struct page reference. This is true iff the address provided is found within the unmapped address range between PAGE_OFFSET & MAP_BASE, but we don't currently check for that condition. Instead we simply mask the address to obtain what will be a physical address if the virtual address is indeed in the desired range, shift it to form a PFN & then call pfn_valid(). This can incorrectly return true if called with a virtual address which, after masking, happens to form a physical address corresponding to a valid PFN. For example we may vmalloc an address in the kernel mapped region starting a MAP_BASE & obtain the virtual address: addr = 0xc000000000002000 When masked by virt_to_phys(), which uses __pa() & in turn CPHYSADDR(), we obtain the following (bogus) physical address: addr = 0x2000 In a common system with PHYS_OFFSET=0 this will correspond to a valid struct page which should really be accessed by virtual address PAGE_OFFSET+0x2000, causing virt_addr_valid() to incorrectly return 1 indicating that the original address corresponds to a struct page. This is equivalent to the ARM64 change made in commitca219452c6
("arm64: Correctly bounds check virt_addr_valid"). This fixes fallout when hardened usercopy is enabled caused by the related commit517e1fbeb6
("mm/usercopy: Drop extra is_vmalloc_or_module() check") which removed a check for the vmalloc range that was present from the introduction of the hardened usercopy feature. Signed-off-by: Paul Burton <paul.burton@mips.com> References:ca219452c6
("arm64: Correctly bounds check virt_addr_valid") References:517e1fbeb6
("mm/usercopy: Drop extra is_vmalloc_or_module() check") Reported-by: Julien Cristau <jcristau@debian.org> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org> Tested-by: YunQiang Su <ysu@wavecomp.com> URL: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=929366 Cc: stable@vger.kernel.org # v4.12+ Cc: linux-mips@vger.kernel.org Cc: Yunqiang Su <ysu@wavecomp.com>
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@ -203,6 +203,11 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
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int __virt_addr_valid(const volatile void *kaddr)
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{
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unsigned long vaddr = (unsigned long)vaddr;
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if ((vaddr < PAGE_OFFSET) || (vaddr >= MAP_BASE))
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return 0;
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return pfn_valid(PFN_DOWN(virt_to_phys(kaddr)));
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}
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EXPORT_SYMBOL_GPL(__virt_addr_valid);
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