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Fri, 05 Feb 2021 09:30:55 -0800 (PST) MIME-Version: 1.0 References: <20210204150100.GE20815@willie-the-truck> <20210204163721.91295-1-lecopzer@gmail.com> <20210205171859.GE22665@willie-the-truck> In-Reply-To: <20210205171859.GE22665@willie-the-truck> From: Andrey Konovalov Date: Fri, 5 Feb 2021 18:30:44 +0100 Message-ID: Subject: Re: [PATCH v2 1/4] arm64: kasan: don't populate vmalloc area for CONFIG_KASAN_VMALLOC To: Will Deacon Cc: Lecopzer Chen , Andrew Morton , Ard Biesheuvel , Andrey Ryabinin , Mark Brown , Catalin Marinas , Dan Williams , Dmitry Vyukov , Alexander Potapenko , gustavoars@kernel.org, kasan-dev , Lecopzer Chen , Linux ARM , LKML , "moderated list:ARM/Mediatek SoC..." , Linux Memory Management List , Guenter Roeck , Robin Murphy , rppt@kernel.org, tyhicks@linux.microsoft.com, Vincenzo Frascino , yj.chiang@mediatek.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 57DB6F9F X-Stat-Signature: kxfgk47cmpzuz7smqx3kwjuq4mz64ucz Received-SPF: none (google.com>: No applicable sender policy available) receiver=imf04; identity=mailfrom; envelope-from=""; helo=mail-pl1-f169.google.com; client-ip=209.85.214.169 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1612546256-450850 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Feb 5, 2021 at 6:19 PM Will Deacon wrote: > > On Fri, Feb 05, 2021 at 12:37:21AM +0800, Lecopzer Chen wrote: > > > > > On Thu, Feb 04, 2021 at 10:46:12PM +0800, Lecopzer Chen wrote: > > > > > On Sat, Jan 09, 2021 at 06:32:49PM +0800, Lecopzer Chen wrote: > > > > > > Linux support KAsan for VMALLOC since commit 3c5c3cfb9ef4da9 > > > > > > ("kasan: support backing vmalloc space with real shadow memory") > > > > > > > > > > > > Like how the MODULES_VADDR does now, just not to early populate > > > > > > the VMALLOC_START between VMALLOC_END. > > > > > > similarly, the kernel code mapping is now in the VMALLOC area and > > > > > > should keep these area populated. > > > > > > > > > > > > Signed-off-by: Lecopzer Chen > > > > > > --- > > > > > > arch/arm64/mm/kasan_init.c | 23 ++++++++++++++++++----- > > > > > > 1 file changed, 18 insertions(+), 5 deletions(-) > > > > > > > > > > > > diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c > > > > > > index d8e66c78440e..39b218a64279 100644 > > > > > > --- a/arch/arm64/mm/kasan_init.c > > > > > > +++ b/arch/arm64/mm/kasan_init.c > > > > > > @@ -214,6 +214,7 @@ static void __init kasan_init_shadow(void) > > > > > > { > > > > > > u64 kimg_shadow_start, kimg_shadow_end; > > > > > > u64 mod_shadow_start, mod_shadow_end; > > > > > > + u64 vmalloc_shadow_start, vmalloc_shadow_end; > > > > > > phys_addr_t pa_start, pa_end; > > > > > > u64 i; > > > > > > > > > > > > @@ -223,6 +224,9 @@ static void __init kasan_init_shadow(void) > > > > > > mod_shadow_start = (u64)kasan_mem_to_shadow((void *)MODULES_VADDR); > > > > > > mod_shadow_end = (u64)kasan_mem_to_shadow((void *)MODULES_END); > > > > > > > > > > > > + vmalloc_shadow_start = (u64)kasan_mem_to_shadow((void *)VMALLOC_START); > > > > > > + vmalloc_shadow_end = (u64)kasan_mem_to_shadow((void *)VMALLOC_END); > > > > > > + > > > > > > /* > > > > > > * We are going to perform proper setup of shadow memory. > > > > > > * At first we should unmap early shadow (clear_pgds() call below). > > > > > > @@ -241,12 +245,21 @@ static void __init kasan_init_shadow(void) > > > > > > > > > > > > kasan_populate_early_shadow(kasan_mem_to_shadow((void *)PAGE_END), > > > > > > (void *)mod_shadow_start); > > > > > > - kasan_populate_early_shadow((void *)kimg_shadow_end, > > > > > > - (void *)KASAN_SHADOW_END); > > > > > > + if (IS_ENABLED(CONFIG_KASAN_VMALLOC)) { > > > > > > > > > > Do we really need yet another CONFIG option for KASAN? What's the use-case > > > > > for *not* enabling this if you're already enabling one of the KASAN > > > > > backends? > > > > > > > > As I know, KASAN_VMALLOC now only supports KASAN_GENERIC and also > > > > KASAN_VMALLOC uses more memory to map real shadow memory (1/8 of vmalloc va). > > > > > > The shadow is allocated dynamically though, isn't it? > > > > Yes, but It's still a cost. > > > > > > There should be someone can enable KASAN_GENERIC but can't use VMALLOC > > > > due to memory issue. > > > > > > That doesn't sound particularly realistic to me. The reason I'm pushing here > > > is because I would _really_ like to move to VMAP stack unconditionally, and > > > that would effectively force KASAN_VMALLOC to be set if KASAN is in use. > > > > > > So unless there's a really good reason not to do that, please can we make > > > this unconditional for arm64? Pretty please? > > > > I think it's fine since we have a good reason. > > Also if someone have memory issue in KASAN_VMALLOC, > > they can use SW_TAG, right? > > > > However the SW_TAG/HW_TAG is not supported VMALLOC yet. > > So the code would be like > > > > if (IS_ENABLED(CONFIG_KASAN_GENERIC)) > > Just make this CONFIG_KASAN_VMALLOC, since that depends on KASAN_GENERIC. > > > /* explain the relationship between > > * KASAN_GENERIC and KASAN_VMALLOC in arm64 > > * XXX: because we want VMAP stack.... > > */ > > I don't understand the relation with SW_TAGS. The VMAP_STACK dependency is: > > depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC This means that VMAP_STACK can be only enabled if KASAN_HW_TAGS=y or if KASAN_VMALLOC=y for other modes. > > which doesn't mention SW_TAGS at all. So that seems to imply that SW_TAGS > and VMAP_STACK are mutually exclusive :( SW_TAGS doesn't yet have vmalloc support, so it's not compatible with VMAP_STACK. Once vmalloc support is added to SW_TAGS, KASAN_VMALLOC should be allowed to be enabled with SW_TAGS. This series is a step towards having that support, but doesn't implement it. That will be a separate effort.