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Fri, 17 Mar 2023 12:26:20 -0700 (PDT) MIME-Version: 1.0 References: <20230227222957.24501-1-rick.p.edgecombe@intel.com> <20230227222957.24501-23-rick.p.edgecombe@intel.com> <236ae66c-fafb-80e9-d58b-6b18a22071c1@intel.com> In-Reply-To: From: Deepak Gupta Date: Fri, 17 Mar 2023 12:26:08 -0700 Message-ID: Subject: Re: [PATCH v7 22/41] mm/mmap: Add shadow stack pages to memory accounting To: "Edgecombe, Rick P" Cc: "Hansen, Dave" , "david@redhat.com" , "bsingharora@gmail.com" , "hpa@zytor.com" , "Syromiatnikov, Eugene" , "peterz@infradead.org" , "rdunlap@infradead.org" , "keescook@chromium.org" , "Yu, Yu-cheng" , "dave.hansen@linux.intel.com" , "kirill.shutemov@linux.intel.com" , "Eranian, Stephane" , "linux-mm@kvack.org" , "fweimer@redhat.com" , "nadav.amit@gmail.com" , "jannh@google.com" , "dethoma@microsoft.com" , "kcc@google.com" , "linux-arch@vger.kernel.org" , "bp@alien8.de" , "oleg@redhat.com" , "hjl.tools@gmail.com" , "pavel@ucw.cz" , "Lutomirski, Andy" , "linux-doc@vger.kernel.org" , "arnd@arndb.de" , "tglx@linutronix.de" , "Schimpe, Christina" , "mike.kravetz@oracle.com" , "x86@kernel.org" , "Yang, Weijiang" , "jamorris@linux.microsoft.com" , "john.allen@amd.com" , "rppt@kernel.org" , "andrew.cooper3@citrix.com" , "mingo@redhat.com" , "corbet@lwn.net" , "linux-kernel@vger.kernel.org" , "linux-api@vger.kernel.org" , "gorcunov@gmail.com" , "akpm@linux-foundation.org" Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: EE666A0012 X-Rspam-User: X-Stat-Signature: c9iwdkjeryqas5qooc4aw17b75d7iy4k X-HE-Tag: 1679081181-618643 X-HE-Meta: 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 b/YtcHml sGdkGXl9APBDEh6sBM0ljifPyl174RcT4ng4PgojHeYwWOcEK8z1tDJWt8jnaSxNMa1F9U9nYf0HbQ4nxMgPofPoiVzlGPBM3i7ztA2GrxdWt28Y3f2R3sIjY4A7vo8emsM0aBTzws9jokCY3AXupRTuE9XHR49gIUjavajZfCeLJz7pmA3a907R8yrnlt+7QYb40BWMDgry/2WRBkD8eaw1hxYPPrSFvCDjI5+bC3t1uTae1GAyLHT52dv2MDKCIjRuhGhmfugc/DdZB6gs749Bj8JtHHv6uo1ZJNrM7uz/PTh1fjw2jc43OXSzBt7bXhE30Yp3wp+T7SaZz3tUkV93IDgb1NsJvatDUhtXXpMziUlHespZ/7l1y9H8uV+WnUKSbHf09R7pnWhBMpP8Eaf+pOF2SHb8oxd/N1b67bBXyO3I= 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, Mar 17, 2023 at 10:42=E2=80=AFAM Edgecombe, Rick P wrote: > > On Fri, 2023-03-17 at 10:28 -0700, Deepak Gupta wrote: > > On Fri, Mar 17, 2023 at 10:16=E2=80=AFAM Dave Hansen > > wrote: > > > > > > On 3/17/23 10:12, Deepak Gupta wrote: > > > > > /* > > > > > - * Stack area - automatically grows in one direction > > > > > + * Stack area > > > > > * > > > > > - * VM_GROWSUP / VM_GROWSDOWN VMAs are always private > > > > > anonymous: > > > > > - * do_mmap() forbids all other combinations. > > > > > + * VM_GROWSUP, VM_GROWSDOWN VMAs are always private > > > > > + * anonymous. do_mmap() forbids all other combinations. > > > > > */ > > > > > static inline bool is_stack_mapping(vm_flags_t flags) > > > > > { > > > > > - return (flags & VM_STACK) =3D=3D VM_STACK; > > > > > + return ((flags & VM_STACK) =3D=3D VM_STACK) || (flags & > > > > > VM_SHADOW_STACK); > > > > > > > > Same comment here. `VM_SHADOW_STACK` is an x86 specific way of > > > > encoding a shadow stack. > > > > Instead let's have a proxy here which allows architectures to > > > > have > > > > their own encodings to represent a shadow stack. > > > > > > This doesn't _preclude_ another architecture from coming along and > > > doing > > > that, right? I'd just prefer that shadow stack architecture #2 > > > comes > > > along and refactors this in precisely the way _they_ need it. > > > > There are two issues here > > - Encoding of shadow stack: Another arch can choose different > > encoding. > > And yes, another architecture can come in and re-factor it. But so > > much thought and work has been given to x86 implementation to keep > > shadow stack to not impact arch agnostic parts of the kernel. So > > why creep it in here. > > > > - VM_SHADOW_STACK is coming out of the VM_HIGH_ARCH_XX bit position > > which makes it arch specific. > > > > > > VM_SHADOW_STACK is defined like this (trimmed for clarity): > #ifdef CONFIG_X86_USER_SHADOW_STACK > # define VM_SHADOW_STACK VM_HIGH_ARCH_5 > #else > # define VM_SHADOW_STACK VM_NONE > #endif Ok. > > Also, we actually had an is_shadow_stack_mapping(vma) in the past, but > it was dropped from other feedback. looks like I've been late to the party. IMHO, that was the right approach. > >