From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io1-f71.google.com (mail-io1-f71.google.com [209.85.166.71]) by kanga.kvack.org (Postfix) with ESMTP id 994B76B026A for ; Wed, 14 Nov 2018 14:23:52 -0500 (EST) Received: by mail-io1-f71.google.com with SMTP id z17-v6so16746245iol.20 for ; Wed, 14 Nov 2018 11:23:52 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id h189-v6sor8358639ioa.35.2018.11.14.11.23.51 for (Google Transport Security); Wed, 14 Nov 2018 11:23:51 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20181107165200.oaou6cx2lmjzmjyl@lakrids.cambridge.arm.com> References: <20181107165200.oaou6cx2lmjzmjyl@lakrids.cambridge.arm.com> From: Andrey Konovalov Date: Wed, 14 Nov 2018 20:23:50 +0100 Message-ID: Subject: Re: [PATCH v10 08/22] kasan, arm64: untag address in __kimg_to_phys and _virt_addr_is_linear Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Mark Rutland 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, "open list:DOCUMENTATION" , LKML , Linux ARM , linux-sparse@vger.kernel.org, Linux Memory Management List , Linux Kbuild mailing list , Kostya Serebryany , Evgeniy Stepanov , Lee Smith , Ramana Radhakrishnan , Jacob Bramley , Ruben Ayrapetyan , Jann Horn , Mark Brand , Chintan Pandya , Vishwath Mohan On Wed, Nov 7, 2018 at 5:52 PM, Mark Rutland wrote: > 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? If kimg address always points into the kernel image, then it shouldn't be tagged, and this can be removed. > >> 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. Will do in v11. > >> + >> #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. __lm_to_phys() does & ~PAGE_OFFSET, so it resets the tag by itself. I can add an explicit __tag_reset() if you think it makes sense. > >> >> #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. Will do in v11. Thanks!