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Message-ID: <d2105690-338e-5285-4b8a-0908e946246a@redhat.com>
Date: Fri, 28 Oct 2016 10:25:44 -0700
From: Laura Abbott <labbott@...hat.com>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Mark Rutland <mark.rutland@....com>,
Will Deacon <will.deacon@....com>,
Catalin Marinas <catalin.marinas@....com>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] arm64: Add support for CONFIG_DEBUG_VIRTUAL
On 10/28/2016 12:52 AM, Ard Biesheuvel wrote:
> Hi Laura,
>
> On 28 October 2016 at 01:18, Laura Abbott <labbott@...hat.com> wrote:
>> x86 has an option CONFIG_DEBUG_VIRTUAL to do additional checks
>> on virt_to_phys calls. The goal is to catch users who are calling
>> virt_to_phys on non-linear addresses immediately. As features
>> such as CONFIG_VMAP_STACK get enabled for arm64, this becomes
>> increasingly important. Add checks to catch bad virt_to_phys
>> usage.
>>
>
> I think this is a useful thing to have. However, the Kconfig
> description talks about virt to page translations, not virt to phys.
> Of course, this is a shift away from being equivalent on x86, but not
> so much on arm64. Any concerns there?
>
I think the description is vague. I'm guessing there were problems
with virt_to_page but the actual check ends up going in virt_to_phys
because that's where the actual problem occurs.
>> Signed-off-by: Laura Abbott <labbott@...hat.com>
>> ---
>> This has been on my TODO list for a while. It caught a few bugs with
>> CONFIG_VMAP_STACK on x86 so when that eventually gets added
>> for arm64 it will be useful to have. This caught one driver calling __pa on an
>> ioremapped address already. RFC for a couple of reasons:
>>
>> 1) This is basically a direct port of the x86 approach.
>> 2) I needed some #ifndef __ASSEMBLY__ which I don't like to throw around.
>> 3) I'm not quite sure about the bounds check for the VIRTUAL_BUG_ON with KASLR,
>> specifically the _end check.
>> 4) Is it worth actually keeping this as DEBUG_VIRTUAL vs. folding it into
>> another option?
>>
>> ---
>> arch/arm64/include/asm/memory.h | 11 ++++++++++-
>> arch/arm64/mm/Makefile | 2 +-
>> arch/arm64/mm/physaddr.c | 17 +++++++++++++++++
>> lib/Kconfig.debug | 2 +-
>> mm/cma.c | 2 +-
>> 5 files changed, 30 insertions(+), 4 deletions(-)
>> create mode 100644 arch/arm64/mm/physaddr.c
>>
>> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
>> index ba62df8..9805adc 100644
>> --- a/arch/arm64/include/asm/memory.h
>> +++ b/arch/arm64/include/asm/memory.h
>> @@ -106,11 +106,19 @@
>> * private definitions which should NOT be used outside memory.h
>> * files. Use virt_to_phys/phys_to_virt/__pa/__va instead.
>> */
>> -#define __virt_to_phys(x) ({ \
>> +#define __virt_to_phys_nodebug(x) ({ \
>> phys_addr_t __x = (phys_addr_t)(x); \
>> __x & BIT(VA_BITS - 1) ? (__x & ~PAGE_OFFSET) + PHYS_OFFSET : \
>> (__x - kimage_voffset); })
>>
>> +#ifdef CONFIG_DEBUG_VIRTUAL
>> +#ifndef __ASSEMBLY__
>> +extern unsigned long __virt_to_phys(unsigned long x);
>> +#endif
>> +#else
>> +#define __virt_to_phys(x) __virt_to_phys_nodebug(x)
>> +#endif
>> +
>
> Couldn't you move this whole block into the #ifndef __ASSEMBLY__
> section lower down in the file?
>
Yes, I think that makes more sense.
>> #define __phys_to_virt(x) ((unsigned long)((x) - PHYS_OFFSET) | PAGE_OFFSET)
>> #define __phys_to_kimg(x) ((unsigned long)((x) + kimage_voffset))
>>
>> @@ -202,6 +210,7 @@ static inline void *phys_to_virt(phys_addr_t x)
>> * Drivers should NOT use these either.
>> */
>> #define __pa(x) __virt_to_phys((unsigned long)(x))
>> +#define __pa_nodebug(x) __virt_to_phys_nodebug((unsigned long)(x))
>> #define __va(x) ((void *)__phys_to_virt((phys_addr_t)(x)))
>> #define pfn_to_kaddr(pfn) __va((pfn) << PAGE_SHIFT)
>> #define virt_to_pfn(x) __phys_to_pfn(__virt_to_phys(x))
>> diff --git a/arch/arm64/mm/Makefile b/arch/arm64/mm/Makefile
>> index 54bb209..bcea84e 100644
>> --- a/arch/arm64/mm/Makefile
>> +++ b/arch/arm64/mm/Makefile
>> @@ -5,6 +5,6 @@ obj-y := dma-mapping.o extable.o fault.o init.o \
>> obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
>> obj-$(CONFIG_ARM64_PTDUMP) += dump.o
>> obj-$(CONFIG_NUMA) += numa.o
>> -
>> +obj-$(CONFIG_DEBUG_VIRTUAL) += physaddr.o
>> obj-$(CONFIG_KASAN) += kasan_init.o
>> KASAN_SANITIZE_kasan_init.o := n
>> diff --git a/arch/arm64/mm/physaddr.c b/arch/arm64/mm/physaddr.c
>> new file mode 100644
>> index 0000000..6c271e2
>> --- /dev/null
>> +++ b/arch/arm64/mm/physaddr.c
>> @@ -0,0 +1,17 @@
>> +#include <linux/mm.h>
>> +
>> +#include <asm/memory.h>
>> +
>> +unsigned long __virt_to_phys(unsigned long x)
>> +{
>> + phys_addr_t __x = (phys_addr_t)x;
>> +
>> + if (__x & BIT(VA_BITS - 1)) {
>> + /* The bit check ensures this is the right range */
>
> Could you expand the comment to clarify that the linear region starts
> right in the middle of the kernel virtual address space, and so we
> only have to test the top bit?
>
Sure.
>> + return (__x & ~PAGE_OFFSET) + PHYS_OFFSET;
>> + } else {l
>> + VIRTUAL_BUG_ON(x < kimage_vaddr || x > (unsigned long)_end);
>
> This looks fine. References to _end are relocated at boot to refer to
> the actual runtime offset.
>
Thanks for clarifying.
>> + return (__x - kimage_voffset);
>> + }
>> +}
>> +EXPORT_SYMBOL(__virt_to_phys);
>> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
>> index 33bc56c..e5634bb 100644
>> --- a/lib/Kconfig.debug
>> +++ b/lib/Kconfig.debug
>> @@ -604,7 +604,7 @@ config DEBUG_VM_PGFLAGS
>>
>> config DEBUG_VIRTUAL
>> bool "Debug VM translations"
>> - depends on DEBUG_KERNEL && X86
>> + depends on DEBUG_KERNEL && (X86 || ARM64)
>> help
>> Enable some costly sanity checks in virtual to page code. This can
>> catch mistakes with virt_to_page() and friends.
>> diff --git a/mm/cma.c b/mm/cma.c
>> index 384c2cb..2345803 100644
>> --- a/mm/cma.c
>> +++ b/mm/cma.c
>> @@ -235,7 +235,7 @@ int __init cma_declare_contiguous(phys_addr_t base,
>> phys_addr_t highmem_start;
>> int ret = 0;
>>
>> -#ifdef CONFIG_X86
>> +#if defined(CONFIG_X86) || defined(CONFIG_ARM64)
>> /*
>> * high_memory isn't direct mapped memory so retrieving its physical
>> * address isn't appropriate. But it would be useful to check the
>> --
>> 2.7.4
>>
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