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Wed, 04 Sep 2024 12:07:16 -0700 (PDT) Date: Wed, 4 Sep 2024 12:07:12 -0700 From: Deepak Gupta To: Mark Brown Cc: "Liam R. Howlett" , Richard Henderson , Ivan Kokshaysky , Matt Turner , Vineet Gupta , Russell King , Guo Ren , Huacai Chen , WANG Xuerui , "James E.J. Bottomley" , Helge Deller , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Naveen N Rao , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , "David S. Miller" , Andreas Larsson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Chris Zankel , Max Filippov , Andrew Morton , Vlastimil Babka , Lorenzo Stoakes , Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-csky@vger.kernel.org, loongarch@lists.linux.dev, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org, Rick Edgecombe Subject: Re: [PATCH 3/3] mm: Care about shadow stack guard gap when getting an unmapped area Message-ID: References: <20240902-mm-generic-shadow-stack-guard-v1-0-9acda38b3dd3@kernel.org> <20240902-mm-generic-shadow-stack-guard-v1-3-9acda38b3dd3@kernel.org> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Post: List-Subscribe: , , List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: On Tue, Sep 03, 2024 at 08:57:20PM +0100, Mark Brown wrote: >On Tue, Sep 03, 2024 at 03:41:49PM -0400, Liam R. Howlett wrote: >> * Mark Brown [240902 15:09]: > >> > +static inline unsigned long stack_guard_placement(vm_flags_t vm_flags) >> > +{ >> > + if (vm_flags & VM_SHADOW_STACK) >> > + return PAGE_SIZE; > >> Is PAGE_SIZE is enough? > >It's what x86 currently uses so it'll be no worse off if it gets moved >to the generic code (there's a comment in the arch code explaing what's >needed there) and it's enough for arm64, we only do single record >pushes/pops or (optionally) writes to unconstrained addresses. It's enough for RISC-V too.