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[2003:cb:c707:4800:aecc:dadb:40a8:ce81]) by smtp.gmail.com with ESMTPSA id 26-20020a05600c229a00b003dc49e0132asm3583198wmf.1.2023.02.21.00.31.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Feb 2023 00:31:12 -0800 (PST) Message-ID: Date: Tue, 21 Feb 2023 09:31:10 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.2 Subject: Re: [PATCH v6 22/41] mm/mmap: Add shadow stack pages to memory accounting To: "Edgecombe, Rick P" , "bsingharora@gmail.com" , "hpa@zytor.com" , "Syromiatnikov, Eugene" , "peterz@infradead.org" , "rdunlap@infradead.org" , "keescook@chromium.org" , "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" , "linux-arch@vger.kernel.org" , "kcc@google.com" , "pavel@ucw.cz" , "oleg@redhat.com" , "hjl.tools@gmail.com" , "bp@alien8.de" , "Lutomirski, Andy" , "linux-doc@vger.kernel.org" , "arnd@arndb.de" , "tglx@linutronix.de" , "Schimpe, Christina" , "x86@kernel.org" , "mike.kravetz@oracle.com" , "Yang, Weijiang" , "debug@rivosinc.com" , "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" Cc: "Yu, Yu-cheng" References: <20230218211433.26859-1-rick.p.edgecombe@intel.com> <20230218211433.26859-23-rick.p.edgecombe@intel.com> <6ccc8d30-336a-12af-1179-5dc4eca3048d@redhat.com> <8bd58778e062bb9526c905c5573a2ee20cb41eef.camel@intel.com> Content-Language: en-US From: David Hildenbrand Organization: Red Hat In-Reply-To: <8bd58778e062bb9526c905c5573a2ee20cb41eef.camel@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20.02.23 23:44, Edgecombe, Rick P wrote: > On Mon, 2023-02-20 at 13:58 +0100, David Hildenbrand wrote: >> On 18.02.23 22:14, Rick Edgecombe wrote: >>> From: Yu-cheng Yu >>> >>> The x86 Control-flow Enforcement Technology (CET) feature includes >>> a new >>> type of memory called shadow stack. This shadow stack memory has >>> some >>> unusual properties, which requires some core mm changes to function >>> properly. >>> >>> Account shadow stack pages to stack memory. >>> >>> Reviewed-by: Kees Cook >>> Tested-by: Pengfei Xu >>> Tested-by: John Allen >>> Signed-off-by: Yu-cheng Yu >>> Co-developed-by: Rick Edgecombe >>> Signed-off-by: Rick Edgecombe >>> Cc: Kees Cook >>> >>> --- >>> v3: >>> - Remove unneeded VM_SHADOW_STACK check in accountable_mapping() >>> (Kirill) >>> >>> v2: >>> - Remove is_shadow_stack_mapping() and just change it to >>> directly bitwise >>> and VM_SHADOW_STACK. >>> >>> Yu-cheng v26: >>> - Remove redundant #ifdef CONFIG_MMU. >>> >>> Yu-cheng v25: >>> - Remove #ifdef CONFIG_ARCH_HAS_SHADOW_STACK for >>> is_shadow_stack_mapping(). >>> --- >>> mm/mmap.c | 2 ++ >>> 1 file changed, 2 insertions(+) >>> >>> diff --git a/mm/mmap.c b/mm/mmap.c >>> index 425a9349e610..9f85596cce31 100644 >>> --- a/mm/mmap.c >>> +++ b/mm/mmap.c >>> @@ -3290,6 +3290,8 @@ void vm_stat_account(struct mm_struct *mm, >>> vm_flags_t flags, long npages) >>> mm->exec_vm += npages; >>> else if (is_stack_mapping(flags)) >>> mm->stack_vm += npages; >>> + else if (flags & VM_SHADOW_STACK) >>> + mm->stack_vm += npages; >> >> Why not modify is_stack_mapping() ? > > It kind of sticks out a little in this conditional, but > is_stack_mapping() has this comment: > /* > * Stack area - automatically grows in one direction > * > * VM_GROWSUP / VM_GROWSDOWN VMAs are always private anonymous: > * do_mmap() forbids all other combinations. > */ > > Shadow stack don't grow, so it doesn't quite fit. There used to be an > is_shadow_stack_mapping(), but it was removed because all that was > needed (for the time being) was the simple bitwise AND: > > https://lore.kernel.org/lkml/804adbac-61e6-0fd2-f726-5735fb290199@intel.com/ As there is only a single user of is_stack_mapping(), I'd simply have adjusted the doc of is_stack_mapping() to include shadow stacks. -- Thanks, David / dhildenb