Messages in this thread | | | Subject | Re: [PATCH v4 1/3] arm64: Improve kernel address detection of __is_lm_address() | From | Vincenzo Frascino <> | Date | Tue, 26 Jan 2021 12:13:57 +0000 |
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On 1/26/21 12:07 PM, Catalin Marinas wrote: > On Tue, Jan 26, 2021 at 11:58:13AM +0000, Vincenzo Frascino wrote: >> On 1/25/21 5:56 PM, Catalin Marinas wrote: >>> On Mon, Jan 25, 2021 at 04:09:57PM +0000, Vincenzo Frascino wrote: >>>> 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. >>> >>> I didn't mean the backport of the whole commit f4693c2716b3 as it >>> probably has other dependencies, just the __is_lm_address() change in >>> that patch. >> >> Then call it preparatory patch ;) > > It's preparatory only for the stable backports, not for current > mainline. But I'd rather change the upstream patch when backporting to > apply cleanly, no need for a preparatory stable patch. >
Thanks for the clarification.
-- Regards, Vincenzo
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