Messages in this thread Patch in this message | | | Date | Thu, 21 Jan 2021 15:12:06 +0000 | From | Mark Rutland <> | Subject | Re: [PATCH v2 1/2] arm64: Fix kernel address detection of __is_lm_address() |
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[adding Ard]
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 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 wonder if it's worth virt_addr_valid() having an explicit check for the kernel VA range, instead.
> 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.
Thanks, Mark.
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