From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi1-f198.google.com (mail-oi1-f198.google.com [209.85.167.198]) by kanga.kvack.org (Postfix) with ESMTP id 2F2606B0524 for ; Wed, 7 Nov 2018 11:52:15 -0500 (EST) Received: by mail-oi1-f198.google.com with SMTP id x6-v6so11192411oig.6 for ; Wed, 07 Nov 2018 08:52:15 -0800 (PST) Received: from foss.arm.com (usa-sjc-mx-foss1.foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id r11si417221oti.216.2018.11.07.08.52.13 for ; Wed, 07 Nov 2018 08:52:13 -0800 (PST) Date: Wed, 7 Nov 2018 16:52:00 +0000 From: Mark Rutland Subject: Re: [PATCH v10 08/22] kasan, arm64: untag address in __kimg_to_phys and _virt_addr_is_linear Message-ID: <20181107165200.oaou6cx2lmjzmjyl@lakrids.cambridge.arm.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Andrey Konovalov Cc: Andrey Ryabinin , Alexander Potapenko , Dmitry Vyukov , Catalin Marinas , Will Deacon , Christoph Lameter , Andrew Morton , Nick Desaulniers , Marc Zyngier , Dave Martin , Ard Biesheuvel , "Eric W . Biederman" , Ingo Molnar , Paul Lawrence , Geert Uytterhoeven , Arnd Bergmann , "Kirill A . Shutemov" , Greg Kroah-Hartman , Kate Stewart , Mike Rapoport , kasan-dev@googlegroups.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-sparse@vger.kernel.org, linux-mm@kvack.org, linux-kbuild@vger.kernel.org, Kostya Serebryany , Evgeniy Stepanov , Lee Smith , Ramana Radhakrishnan , Jacob Bramley , Ruben Ayrapetyan , Jann Horn , Mark Brand , Chintan Pandya , Vishwath Mohan Hi Andrey, On Tue, Nov 06, 2018 at 06:30:23PM +0100, Andrey Konovalov wrote: > __kimg_to_phys (which is used by virt_to_phys) and _virt_addr_is_linear > (which is used by virt_addr_valid) assume that the top byte of the address > is 0xff, which isn't always the case with tag-based KASAN. I'm confused by this. Why/when do kimg address have a non-default tag? Any kimg address is part of the static kernel image, so it's not obvious to me how a kimg address would gain a tag. Could you please explain how this happens in the commit message? > This patch resets the tag in those macros. > > Reviewed-by: Andrey Ryabinin > Reviewed-by: Dmitry Vyukov > Signed-off-by: Andrey Konovalov > --- > arch/arm64/include/asm/memory.h | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h > index 0f1e024a951f..3226a0218b0b 100644 > --- a/arch/arm64/include/asm/memory.h > +++ b/arch/arm64/include/asm/memory.h > @@ -92,6 +92,15 @@ > #define KASAN_THREAD_SHIFT 0 > #endif > > +#ifdef CONFIG_KASAN_SW_TAGS > +#define KASAN_TAG_SHIFTED(tag) ((unsigned long)(tag) << 56) > +#define KASAN_SET_TAG(addr, tag) (((addr) & ~KASAN_TAG_SHIFTED(0xff)) | \ > + KASAN_TAG_SHIFTED(tag)) > +#define KASAN_RESET_TAG(addr) KASAN_SET_TAG(addr, 0xff) > +#else > +#define KASAN_RESET_TAG(addr) addr > +#endif Nit: the rest of the helper macros in this file are lower-case, with specialised helpers prefixed with several underscores. Could we please stick with that convention? e.g. have __tag_set() and __tag_reset() helpers. > + > #define MIN_THREAD_SHIFT (14 + KASAN_THREAD_SHIFT) > > /* > @@ -232,7 +241,7 @@ static inline unsigned long kaslr_offset(void) > #define __is_lm_address(addr) (!!((addr) & BIT(VA_BITS - 1))) > > #define __lm_to_phys(addr) (((addr) & ~PAGE_OFFSET) + PHYS_OFFSET) > -#define __kimg_to_phys(addr) ((addr) - kimage_voffset) > +#define __kimg_to_phys(addr) (KASAN_RESET_TAG(addr) - kimage_voffset) IIUC You need to adjust __lm_to_phys() too, since that could be passed an address from SLAB. Maybe that's done in a later patch, but if so it's confusing to split it out that way. It would be nicer to fix all the *_to_*() helpers in one go. > > #define __virt_to_phys_nodebug(x) ({ \ > phys_addr_t __x = (phys_addr_t)(x); \ > @@ -308,7 +317,8 @@ static inline void *phys_to_virt(phys_addr_t x) > #endif > #endif > > -#define _virt_addr_is_linear(kaddr) (((u64)(kaddr)) >= PAGE_OFFSET) > +#define _virt_addr_is_linear(kaddr) (KASAN_RESET_TAG((u64)(kaddr)) >= \ > + PAGE_OFFSET) This is painful to read. Could you please split this like: #define _virt_addr_is_linear(kaddr) \ (__tag_reset((u64)(kaddr)) >= PAGE_OFFSET) ... and we could reformat virt_addr_valid() in the same way while we're at it. Thanks, Mark.