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Wed, 23 Apr 2025 17:45:57 -0700 (PDT) Date: Wed, 23 Apr 2025 17:45:53 -0700 From: Deepak Gupta To: Radim =?utf-8?B?S3LEjW3DocWZ?= Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Lorenzo Stoakes , Paul Walmsley , Palmer Dabbelt , Albert Ou , Conor Dooley , Rob Herring , Krzysztof Kozlowski , Arnd Bergmann , Christian Brauner , Peter Zijlstra , Oleg Nesterov , Eric Biederman , Kees Cook , Jonathan Corbet , Shuah Khan , Jann Horn , Conor Dooley , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, devicetree@vger.kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, alistair.francis@wdc.com, richard.henderson@linaro.org, jim.shu@sifive.com, andybnac@gmail.com, kito.cheng@sifive.com, charlie@rivosinc.com, atishp@rivosinc.com, evan@rivosinc.com, cleger@rivosinc.com, alexghiti@rivosinc.com, samitolvanen@google.com, broonie@kernel.org, rick.p.edgecombe@intel.com, Zong Li , linux-riscv Subject: Re: [PATCH v12 06/28] riscv/mm : ensure PROT_WRITE leads to VM_READ | VM_WRITE Message-ID: References: <20250314-v5_user_cfi_series-v12-0-e51202b53138@rivosinc.com> <20250314-v5_user_cfi_series-v12-6-e51202b53138@rivosinc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: A8B1C40004 X-Stat-Signature: k6547ogefq1tpx3z54beajaukwcn1kao X-HE-Tag: 1745455558-216989 X-HE-Meta: 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 RJu9L0Jt 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 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: List-Subscribe: List-Unsubscribe: On Thu, Apr 10, 2025 at 12:03:44PM +0200, Radim Krčmář wrote: >2025-03-14T14:39:25-07:00, Deepak Gupta : >> diff --git a/arch/riscv/include/asm/mman.h b/arch/riscv/include/asm/mman.h >> +static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot, >> + unsigned long pkey __always_unused) >> +{ >> + unsigned long ret = 0; >> + >> + /* >> + * If PROT_WRITE was specified, force it to VM_READ | VM_WRITE. >> + * Only VM_WRITE means shadow stack. >> + */ > >This function also changes PROT_WX to VM_RWX, which is effectively not >changing anything, but I think it deserves an explicit intent. >(At least in the commit message.) Will do that. > >> + if (prot & PROT_WRITE) >> + ret = (VM_READ | VM_WRITE); >> + return ret; >> +} >> diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c >> @@ -16,6 +17,15 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len, >> + /* >> + * If PROT_WRITE is specified then extend that to PROT_READ >> + * protection_map[VM_WRITE] is now going to select shadow stack encodings. >> + * So specifying PROT_WRITE actually should select protection_map [VM_WRITE | VM_READ] >> + * If user wants to create shadow stack then they should use `map_shadow_stack` syscall. >> + */ >> + if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ))) >> + prot |= PROT_READ; > >Why isn't the previous hunk be enough? (Or why don't we do just this?) > >riscv_sys_mmap() eventually calls arch_calc_vm_prot_bits(), so I'd >rather fix each code path just once. You're right. Above hunk (arch/riscv/include/asm/mman.h) alone should be enough. I did this change in `sys_riscv.c` out of caution. If it feels like un-necessary, I'll remove it. No hard feelings either way. > >Thanks.