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Fri, 15 Jan 2021 12:01:28 -0500 Received: from mail-pg1-x529.google.com (mail-pg1-x529.google.com [IPv6:2607:f8b0:4864:20::529]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 27ADAC061757 for ; Fri, 15 Jan 2021 09:00:48 -0800 (PST) Received: by mail-pg1-x529.google.com with SMTP id n10so6352312pgl.10 for ; Fri, 15 Jan 2021 09:00:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=PpClgSgoL5qlpfbaIDgx+JiK7CY1YGls1Kpu5D2pXJM=; b=uyCixVTzoIdCHTSe73V5pVNgDxg9Tc74jsDQCYZviBWeWUEbZMNEktX9LrepMGaYU7 tnxspVujy3IKRPQOO6zcRWDPT26Mg7w+JuuiRmDz+K9loh/hhiVX7nRo+gZe933/541V c37METKgJmpTGM+GebawsbqaGafQRtZcEr+Il2S7j4V6DMMHdfh3ZxS1oLRtKbnSu7Lm eMkG33dh/bhPlWCEOqxjzIwcZ3bzkggOf6hbETA+P71OQTY1DAR6O9v9um/KU/oQph70 fy3MvHLGCjJDRymq6Z8cGbTY+oUv889luwLB5aU5NJo4uiNb8Q8IRH94P8z51AfdTad4 AR6Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=PpClgSgoL5qlpfbaIDgx+JiK7CY1YGls1Kpu5D2pXJM=; b=EJjQE8cR1bu4jJMTh+t8VtBRJaSQ900rCoReOP0DIV6gOv66o6WGkeHH52NfgrKkKM qCaNLS0I2qAfyzCi/9I3EJOZoKkeMjPlmq1cbDenK8ocYVplJZ7ZgSSYQxSqbmxBNH/0 wLgvm2ItWHrsIwqZqkjArZ6PbKH6/LpuP+E1id9Fa+sPRwGRIA63SRs8odPDySP3nATq yMqiUa33sYxlwr19T/yANONPiYEGacab8Dh3mBkbOgpAfInYyKkRBR7r/8BzSwOG0Voc VKhEhw/pnAezqAi0I4cAZjXg7zn8PLql+Q+fkDlwuv/uymgm4pyPWn/Kyw7FdV7HYzOg tToQ== X-Gm-Message-State: AOAM530frwbwuK3YhHeRBKdI0+Oyp9ICYcn7rmXqiXKlnBf+b25ebsz3 TZEr03V6s65r2Bw21bStsjLvAZD8rw6bIgmeObJH/w== X-Google-Smtp-Source: ABdhPJwhvahtE9d/id+FvyRynN9rz4lvtkignWGxUEkpYTA/x0WQhQ3wphGYDQ3Rgn2Cr058ucCafMD+GA+cb7whaMs= X-Received: by 2002:a62:e309:0:b029:1ae:5b4a:3199 with SMTP id g9-20020a62e3090000b02901ae5b4a3199mr13254266pfh.24.1610730047501; Fri, 15 Jan 2021 09:00:47 -0800 (PST) MIME-Version: 1.0 References: <1965508bcbec62699715d32bef91628ef55b4b44.1610553774.git.andreyknvl@google.com> <20210113165441.GC27045@gaia> <20210115165558.GF16707@gaia> In-Reply-To: <20210115165558.GF16707@gaia> From: Andrey Konovalov Date: Fri, 15 Jan 2021 18:00:36 +0100 Message-ID: Subject: Re: [PATCH 2/2] kasan, arm64: fix pointer tags in KASAN reports To: Catalin Marinas Cc: Vincenzo Frascino , Dmitry Vyukov , Alexander Potapenko , Marco Elver , Andrew Morton , Will Deacon , Andrey Ryabinin , Peter Collingbourne , Evgenii Stepanov , Branislav Rankov , Kevin Brodsky , kasan-dev , Linux ARM , Linux Memory Management List , LKML Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 15, 2021 at 5:56 PM Catalin Marinas wrote: > > On Fri, Jan 15, 2021 at 05:30:40PM +0100, Andrey Konovalov wrote: > > On Wed, Jan 13, 2021 at 5:54 PM Catalin Marinas wrote: > > > On Wed, Jan 13, 2021 at 05:03:30PM +0100, Andrey Konovalov wrote: > > > > As of the "arm64: expose FAR_EL1 tag bits in siginfo" patch, the address > > > > that is passed to report_tag_fault has pointer tags in the format of 0x0X, > > > > while KASAN uses 0xFX format (note the difference in the top 4 bits). > > > > > > > > Fix up the pointer tag before calling kasan_report. > > > > > > > > Link: https://linux-review.googlesource.com/id/I9ced973866036d8679e8f4ae325de547eb969649 > > > > Fixes: dceec3ff7807 ("arm64: expose FAR_EL1 tag bits in siginfo") > > > > Fixes: 4291e9ee6189 ("kasan, arm64: print report from tag fault handler") > > > > Signed-off-by: Andrey Konovalov > > > > --- > > > > arch/arm64/mm/fault.c | 2 ++ > > > > 1 file changed, 2 insertions(+) > > > > > > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > > > > index 3c40da479899..a218f6f2fdc8 100644 > > > > --- a/arch/arm64/mm/fault.c > > > > +++ b/arch/arm64/mm/fault.c > > > > @@ -304,6 +304,8 @@ static void report_tag_fault(unsigned long addr, unsigned int esr, > > > > { > > > > bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0; > > > > > > > > + /* The format of KASAN tags is 0xF. */ > > > > + addr |= (0xF0UL << MTE_TAG_SHIFT); > > > > > > Ah, I see, that top 4 bits are zeroed by do_tag_check_fault(). When this > > > was added, the only tag faults were generated for user addresses. > > > > > > Anyway, I'd rather fix it in there based on bit 55, something like (only > > > compile-tested): > > > > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > > > index 3c40da479899..2b71079d2d32 100644 > > > --- a/arch/arm64/mm/fault.c > > > +++ b/arch/arm64/mm/fault.c > > > @@ -709,10 +709,11 @@ static int do_tag_check_fault(unsigned long far, unsigned int esr, > > > struct pt_regs *regs) > > > { > > > /* > > > - * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN for tag > > > - * check faults. Mask them out now so that userspace doesn't see them. > > > + * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN > > > + * for tag check faults. Set them to the corresponding bits in the > > > + * untagged address. > > > */ > > > - far &= (1UL << 60) - 1; > > > + far = (untagged_addr(far) & ~MTE_TAG_MASK) | (far & MTE_TAG_MASK) ; > > > do_bad_area(far, esr, regs); > > > return 0; > > > } > > > > BTW, we can do "untagged_addr(far) | (far & MTE_TAG_MASK)" here, as > > untagged_addr() doesn't change kernel pointers. > > untagged_addr() does change tagged kernel pointers, it sign-extends from > bit 55. So the top byte becomes 0xff and you can no longer or the tag > bits in. That's __untagged_addr(), untagged_addr() keeps the bits for kernel pointers as of 597399d0cb91.