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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> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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.