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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Uladzislau Rezki , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrey Konovalov , Marco Elver , Vincenzo Frascino , Peter Collingbourne , Will Deacon , Ryan.Roberts@arm.com, david.hildenbrand@arm.com Subject: Re: [PATCH v2 2/3] kasan: skip HW tagging for all kernel thread stacks Message-ID: References: <20260324132631.482520-1-usama.anjum@arm.com> <20260324132631.482520-3-usama.anjum@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260324132631.482520-3-usama.anjum@arm.com> X-Stat-Signature: onhaqb3t1y3ekqpc5a9ck76ryjjksgqo X-Rspamd-Queue-Id: 3CCF98000C X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1775845950-487041 X-HE-Meta: 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 8/bqEYML lIuk5wmQc17/wGKhMi0qiX9RnMjbcnoPoe7UBZj7x4tHQ1nT4k2Dvcu1UZMtKb/DqFmoxw755OoAPyZM4v5DcbBgLOa5Vx8RPwx234EeCIsOEJZucMVuum4Ll6ZfBs0//76Rwg9zc6wYZH4mOqxHCUWzhdgZFPwVAxUasFynAWKqpm5SpgTsDsPhRX1j1CH+k7ffoEHyVft4ngnpVchKSNJ9haxnjVNP+Y6zzJvHAMS3/bmnLHtlKj97rYSAGoIYsuXUXsdDdoeRvHD0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 24, 2026 at 01:26:28PM +0000, Muhammad Usama Anjum wrote: > diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h > index 051e429026904..307b8390fc670 100644 > --- a/include/linux/thread_info.h > +++ b/include/linux/thread_info.h > @@ -92,7 +92,7 @@ static inline long set_restart_fn(struct restart_block *restart, > #define THREAD_ALIGN THREAD_SIZE > #endif > > -#define THREADINFO_GFP (GFP_KERNEL_ACCOUNT | __GFP_ZERO) > +#define THREADINFO_GFP (GFP_KERNEL_ACCOUNT | __GFP_ZERO | __GFP_SKIP_KASAN) > > /* > * flag set/clear/test wrappers > diff --git a/kernel/fork.c b/kernel/fork.c > index bb0c2613a5604..4bc7a03662109 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -207,7 +207,7 @@ static DEFINE_PER_CPU(struct vm_struct *, cached_stacks[NR_CACHED_STACKS]); > * accounting is performed by the code assigning/releasing stacks to tasks. > * We need a zeroed memory without __GFP_ACCOUNT. > */ > -#define GFP_VMAP_STACK (GFP_KERNEL | __GFP_ZERO) > +#define GFP_VMAP_STACK (GFP_KERNEL | __GFP_ZERO | __GFP_SKIP_KASAN) > > struct vm_stack { > struct rcu_head rcu; > @@ -345,7 +345,8 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node) > } > > /* Reset stack metadata. */ > - kasan_unpoison_range(vm_area->addr, THREAD_SIZE); > + if (!kasan_hw_tags_enabled()) > + kasan_unpoison_range(vm_area->addr, THREAD_SIZE); > > stack = kasan_reset_tag(vm_area->addr); I wonder, since with kasan_reset_tag() returns a match-all pointer even with KASAN_SW_TAGS, is it worth unpoisoning the range (unless it somehow interferes with vfree() but I couldn't see how). What the original approach might help with is use-after-realloc in case we had a tagged pointer in a past life of a page and it still works now. Oh well, that's I guess for other types of hardening to address like delayed reallocation. -- Catalin