Messages in this thread | | | Subject | Re: [PATCH v4 1/3] arm64: Improve kernel address detection of __is_lm_address() | From | Vincenzo Frascino <> | Date | Mon, 25 Jan 2021 16:09:57 +0000 |
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On 1/25/21 2:59 PM, Catalin Marinas wrote: > On Mon, Jan 25, 2021 at 02:36:34PM +0000, Vincenzo Frascino wrote: >> On 1/25/21 1:02 PM, Mark Rutland wrote: >>> On Fri, Jan 22, 2021 at 03:56:40PM +0000, Vincenzo Frascino wrote: >>>> Currently, the __is_lm_address() check just masks out the top 12 bits >>>> of the address, but if they are 0, it still yields a true result. >>>> This has as a side effect that virt_addr_valid() returns true even for >>>> invalid virtual addresses (e.g. 0x0). >>>> >>>> Improve the detection checking that it's actually a kernel address >>>> starting at PAGE_OFFSET. >>>> >>>> Cc: Catalin Marinas <catalin.marinas@arm.com> >>>> Cc: Will Deacon <will@kernel.org> >>>> Suggested-by: Catalin Marinas <catalin.marinas@arm.com> >>>> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> >>>> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> >>> >>> Looking around, it seems that there are some existing uses of >>> virt_addr_valid() that expect it to reject addresses outside of the >>> TTBR1 range. For example, check_mem_type() in drivers/tee/optee/call.c. >>> >>> Given that, I think we need something that's easy to backport to stable. >>> >> >> I agree, I started looking at it this morning and I found cases even in the main >> allocators (slub and page_alloc) either then the one you mentioned. >> >>> This patch itself looks fine, but it's not going to backport very far, >>> so I suspect we might need to write a preparatory patch that adds an >>> explicit range check to virt_addr_valid() which can be trivially >>> backported. >>> >> >> I checked the old releases and I agree this is not back-portable as it stands. >> I propose therefore to add a preparatory patch with the check below: >> >> #define __is_ttrb1_address(addr) ((u64)(addr) >= PAGE_OFFSET && \ >> (u64)(addr) < PAGE_END) >> >> If it works for you I am happy to take care of it and post a new version of my >> patches. > > I'm not entirely sure we need a preparatory patch. IIUC (it needs > checking), virt_addr_valid() was fine until 5.4, broken by commit > 14c127c957c1 ("arm64: mm: Flip kernel VA space"). Will addressed the > flip case in 68dd8ef32162 ("arm64: memory: Fix virt_addr_valid() using > __is_lm_address()") but this broke the <PAGE_OFFSET case. So in 5.4 a > NULL address is considered valid. > > Ard's commit f4693c2716b3 ("arm64: mm: extend linear region for 52-bit > VA configurations") changed the test to no longer rely on va_bits but > did not change the broken semantics. > > If Ard's change plus the fix proposed in this test works on 5.4, I'd say > we just merge this patch with the corresponding Cc stable and Fixes tags > and tweak it slightly when doing the backports as it wouldn't apply > cleanly. IOW, I wouldn't add another check to virt_addr_valid() as we > did not need one prior to 5.4. >
Thank you for the detailed analysis. I checked on 5.4 and it seems that Ard patch (not a clean backport) plus my proposed fix works correctly and solves the issue.
Tomorrow I will post a new version of the series that includes what you are suggesting.
-- Regards, Vincenzo
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