From nobody Sun Dec 14 17:58:00 2025 Received: from mail-10630.protonmail.ch (mail-10630.protonmail.ch [79.135.106.30]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CA0013590D5 for ; Wed, 29 Oct 2025 20:11:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=79.135.106.30 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761768673; cv=none; b=O5od0cQXvGn8jc5ZH5FFk2GxqXbu3oH6z5lXXNMdzdpkFN5Xv5M6Zwt+Adc6fBsJRDzj4AGrtqqENB6gyk202AulOVLU2iMwJnHSgQkC9lVOQg4lZFF4WiJrNBSanegkCjKNnaIwAOhq4P/DmmCrkYUmwmIZJBQ10BVuvLTy3zc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761768673; c=relaxed/simple; bh=j2uwSocT6IFw6bbQ1grp87Y3SKSODbUdA2TcfR9tSV8=; h=Date:To:From:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=BTGm++xACNV5CVsnH3QVrZivCgGoM6yB37uAsybTh+kviKgHWUXZ5JZIVLHz9m26kM7m405G8l+PFKNi8ow+EMrkJwnxCQasWfC2jAEXC+A2XuKqFeKFnl7RvpsTgeSJNqIPM9lNVnxe3xM43gS5UOkNegPpshUVU50Z3+1PnQ8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=pm.me; spf=pass smtp.mailfrom=pm.me; dkim=pass (2048-bit key) header.d=pm.me header.i=@pm.me header.b=fzcdT/Mg; arc=none smtp.client-ip=79.135.106.30 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=pm.me Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=pm.me Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=pm.me header.i=@pm.me header.b="fzcdT/Mg" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pm.me; s=protonmail3; t=1761768667; x=1762027867; bh=qpGuNHZZR4hchfLUKKttSmaxG+W37eMF01r5+dBbCBY=; h=Date:To:From:Cc:Subject:Message-ID:In-Reply-To:References: Feedback-ID:From:To:Cc:Date:Subject:Reply-To:Feedback-ID: Message-ID:BIMI-Selector; b=fzcdT/Mg837dtUDPzN3IZvJaFmIR4Koi9D+v6niFRb/NDXYCqERKygFXgJXDi25Nv opesT+yY+ZAJxBCKk0ZbHNPb4MmR/qTVK0Z2Q1fl5bY9rdus7GvFftgsKs92S3Qtzm u8mvfXIT3aHxC5vDZBVshhQgdWJHoFxaxEJQtYDzMAhElAG7KvcXieapyAoWHrlRUN yJpUT363OVIiMLTqvxO9wi+6g5bah1gyRFRfq8Q1ReHcFkouvWUfWHp20CeXzhITsI U97+N2r0KUpsSmw9ebJH+rNIrUxQ1hFJolDaiMg/U/CTV4shVJNvcKz19+T0ukaPqk nmoReRkSuQ50g== Date: Wed, 29 Oct 2025 20:11:00 +0000 To: xin@zytor.com, peterz@infradead.org, kaleshsingh@google.com, kbingham@kernel.org, akpm@linux-foundation.org, nathan@kernel.org, ryabinin.a.a@gmail.com, dave.hansen@linux.intel.com, bp@alien8.de, morbo@google.com, jeremy.linton@arm.com, smostafa@google.com, kees@kernel.org, baohua@kernel.org, vbabka@suse.cz, justinstitt@google.com, wangkefeng.wang@huawei.com, leitao@debian.org, jan.kiszka@siemens.com, fujita.tomonori@gmail.com, hpa@zytor.com, urezki@gmail.com, ubizjak@gmail.com, ada.coupriediaz@arm.com, nick.desaulniers+lkml@gmail.com, ojeda@kernel.org, brgerst@gmail.com, elver@google.com, pankaj.gupta@amd.com, glider@google.com, mark.rutland@arm.com, trintaeoitogc@gmail.com, jpoimboe@kernel.org, thuth@redhat.com, pasha.tatashin@soleen.com, dvyukov@google.com, jhubbard@nvidia.com, catalin.marinas@arm.com, yeoreum.yun@arm.com, mhocko@suse.com, lorenzo.stoakes@oracle.com, samuel.holland@sifive.com, vincenzo.frascino@arm.com, bigeasy@linutronix.de, surenb@google.com, ardb@kernel.org, Liam.Howlett@oracle.com, nicolas.schier@linux.dev, ziy@nvidia.com, kas@kernel.org, tglx@linutronix.de, mingo@redhat.com, broonie@kernel.org, corbet@lwn.net, andreyknvl@gmail.com, maciej.wieczor-retman@intel.com, david@redhat.com, maz@kernel.org, rppt@kernel.org, will@kernel.org, luto@kernel.org From: Maciej Wieczor-Retman Cc: kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, linux-kbuild@vger.kernel.org, linux-mm@kvack.org, llvm@lists.linux.dev, linux-doc@vger.kernel.org, m.wieczorretman@pm.me Subject: [PATCH v6 17/18] x86/kasan: Logical bit shift for kasan_mem_to_shadow Message-ID: <81848c9df2dc22e9d9104c8276879e6e849a5087.1761763681.git.m.wieczorretman@pm.me> In-Reply-To: References: Feedback-ID: 164464600:user:proton X-Pm-Message-ID: 1962ec27b7155c20b7f866d92710251ffdf5f53c Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Maciej Wieczor-Retman While generally tag-based KASAN adopts an arithemitc bit shift to convert a memory address to a shadow memory address, it doesn't work for all cases on x86. Testing different shadow memory offsets proved that either 4 or 5 level paging didn't work correctly or inline mode ran into issues. Thus the best working scheme is the logical bit shift and non-canonical shadow offset that x86 uses for generic KASAN, of course adjusted for the increased granularity from 8 to 16 bytes. Add an arch specific implementation of kasan_mem_to_shadow() that uses the logical bit shift. The non-canonical hook tries to calculate whether an address came from kasan_mem_to_shadow(). First it checks whether this address fits into the legal set of values possible to output from the mem to shadow function. Tie both generic and tag-based x86 KASAN modes to the address range check associated with generic KASAN. Signed-off-by: Maciej Wieczor-Retman --- Changelog v4: - Add this patch to the series. arch/x86/include/asm/kasan.h | 7 +++++++ mm/kasan/report.c | 5 +++-- 2 files changed, 10 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/kasan.h b/arch/x86/include/asm/kasan.h index 375651d9b114..2372397bc3e5 100644 --- a/arch/x86/include/asm/kasan.h +++ b/arch/x86/include/asm/kasan.h @@ -49,6 +49,13 @@ #include =20 #ifdef CONFIG_KASAN_SW_TAGS +static inline void *__kasan_mem_to_shadow(const void *addr) +{ + return (void *)((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT) + + KASAN_SHADOW_OFFSET; +} + +#define kasan_mem_to_shadow(addr) __kasan_mem_to_shadow(addr) #define __tag_shifted(tag) FIELD_PREP(GENMASK_ULL(60, 57), tag) #define __tag_reset(addr) (sign_extend64((u64)(addr), 56)) #define __tag_get(addr) ((u8)FIELD_GET(GENMASK_ULL(60, 57), (u64)addr)) diff --git a/mm/kasan/report.c b/mm/kasan/report.c index 50d487a0687a..fd8fe004b0c0 100644 --- a/mm/kasan/report.c +++ b/mm/kasan/report.c @@ -642,13 +642,14 @@ void kasan_non_canonical_hook(unsigned long addr) const char *bug_type; =20 /* - * For Generic KASAN, kasan_mem_to_shadow() uses the logical right shift + * For Generic KASAN and Software Tag-Based mode on the x86 + * architecture, kasan_mem_to_shadow() uses the logical right shift * and never overflows with the chosen KASAN_SHADOW_OFFSET values (on * both x86 and arm64). Thus, the possible shadow addresses (even for * bogus pointers) belong to a single contiguous region that is the * result of kasan_mem_to_shadow() applied to the whole address space. */ - if (IS_ENABLED(CONFIG_KASAN_GENERIC)) { + if (IS_ENABLED(CONFIG_KASAN_GENERIC) || IS_ENABLED(CONFIG_X86_64)) { if (addr < (unsigned long)kasan_mem_to_shadow((void *)(0UL)) || addr > (unsigned long)kasan_mem_to_shadow((void *)(~0UL))) return; --=20 2.51.0