Messages in this thread | | | Subject | Re: [PATCH v2 1/2] arm64: Fix kernel address detection of __is_lm_address() | From | Vincenzo Frascino <> | Date | Thu, 21 Jan 2021 15:30:51 +0000 |
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On 1/21/21 3:12 PM, Mark Rutland wrote: > [adding Ard] >
Thanks for this, it is related to his patch and I forgot to Cc: him directly.
> On Thu, Jan 21, 2021 at 01:19:55PM +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). > > When it was added, __is_lm_address() was intended to distinguish valid > kernel virtual addresses (i.e. those in the TTBR1 address range), and > wasn't intended to do anything for addresses outside of this range. See > commit: > > ec6d06efb0bac6cd ("arm64: Add support for CONFIG_DEBUG_VIRTUAL") > > ... where it simply tests a bit. > > So I believe that it's working as intended (though this is poorly > documented), but I think you're saying that usage isn't aligned with > that intent. Given that, I'm not sure the fixes tag is right; I think it > has never had the semantic you're after. >
I did not do much thinking on the intended semantics. I based my interpretation on what you are saying (the usage is not aligned with the intent). Based on what you are are saying, I will change the patch description removing the "Fix" term.
> I had thought the same was true for virt_addr_valid(), and that wasn't > expected to be called for VAs outside of the kernel VA range. Is it > actually safe to call that with NULL on other architectures? >
I am not sure on this, did not do any testing outside of arm64.
> I wonder if it's worth virt_addr_valid() having an explicit check for > the kernel VA range, instead. >
I have no strong opinion either way even if personally I feel that modifying __is_lm_address() is more clear. Feel free to propose something.
>> Fix the detection checking that it's actually a kernel address starting >> at PAGE_OFFSET. >> >> Fixes: f4693c2716b35 ("arm64: mm: extend linear region for 52-bit VA configurations") >> Cc: Catalin Marinas <catalin.marinas@arm.com> >> Cc: Will Deacon <will@kernel.org> >> Suggested-by: Catalin Marinas <catalin.marinas@arm.com> >> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> >> --- >> arch/arm64/include/asm/memory.h | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h >> index 18fce223b67b..e04ac898ffe4 100644 >> --- a/arch/arm64/include/asm/memory.h >> +++ b/arch/arm64/include/asm/memory.h >> @@ -249,7 +249,7 @@ static inline const void *__tag_set(const void *addr, u8 tag) >> /* >> * The linear kernel range starts at the bottom of the virtual address space. >> */ >> -#define __is_lm_address(addr) (((u64)(addr) & ~PAGE_OFFSET) < (PAGE_END - PAGE_OFFSET)) >> +#define __is_lm_address(addr) (((u64)(addr) ^ PAGE_OFFSET) < (PAGE_END - PAGE_OFFSET)) > > If we're going to make this stronger, can we please expand the comment > with the intended semantic? Otherwise we're liable to break this in > future. >
Based on your reply on the above matter, if you agree, I am happy to extend the comment.
> Thanks, > Mark. >
-- Regards, Vincenzo
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