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Edgecombe" , Deepak Gupta , Ard Biesheuvel , Szabolcs Nagy , Kees Cook , "H.J. Lu" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Florian Weimer , Christian Brauner , Ross Burton , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org Subject: Re: [PATCH v9 20/39] arm64/gcs: Ensure that new threads have a GCS In-Reply-To: <20240625-arm64-gcs-v9-20-0f634469b8f0@kernel.org> (Mark Brown's message of "Tue, 25 Jun 2024 15:57:48 +0100") References: <20240625-arm64-gcs-v9-0-0f634469b8f0@kernel.org> <20240625-arm64-gcs-v9-20-0f634469b8f0@kernel.org> Date: Tue, 16 Jul 2024 23:05:04 -0300 Message-ID: <87bk2wu627.fsf@linaro.org> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Mark Brown writes: > diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c > index b0a67efc522b..4a3ce8e3bdfb 100644 > --- a/arch/arm64/mm/gcs.c > +++ b/arch/arm64/mm/gcs.c > @@ -8,6 +8,139 @@ > #include > #include > > +static unsigned long alloc_gcs(unsigned long addr, unsigned long size, > + unsigned long token_offset, bool set_res_tok) The token_offset and set_res_tok arguments aren't used in this function, so they can be removed. > +{ > + int flags = MAP_ANONYMOUS | MAP_PRIVATE; > + struct mm_struct *mm = current->mm; > + unsigned long mapped_addr, unused; > + > + if (addr) > + flags |= MAP_FIXED_NOREPLACE; > + > + mmap_write_lock(mm); > + mapped_addr = do_mmap(NULL, addr, size, PROT_READ | PROT_WRITE, flags, > + VM_SHADOW_STACK, 0, &unused, NULL); > + mmap_write_unlock(mm); > + > + return mapped_addr; > +} > + > +static unsigned long gcs_size(unsigned long size) > +{ > + if (size) > + return PAGE_ALIGN(size); > + > + /* Allocate RLIMIT_STACK/2 with limits of PAGE_SIZE..2G */ > + size = PAGE_ALIGN(min_t(unsigned long long, > + rlimit(RLIMIT_STACK) / 2, SZ_2G)); > + return max(PAGE_SIZE, size); > +} > + > +static bool gcs_consume_token(struct mm_struct *mm, unsigned long user_addr) > +{ > + u64 expected = GCS_CAP(user_addr); > + u64 val; > + int ret; > + > + /* This should really be an atomic cpmxchg. It is not. */ s/cpmxchg/cmpxchg/ The same typo is also in arch/x86/kernel/shstk.c, from the "fork: Support shadow stacks in clone3()" patch series. > + ret = access_remote_vm(mm, user_addr, &val, sizeof(val), > + FOLL_FORCE); > + if (ret != sizeof(val)) > + return false; > + > + if (val != expected) > + return false; > + > + val = 0; > + ret = access_remote_vm(mm, user_addr, &val, sizeof(val), > + FOLL_FORCE | FOLL_WRITE); > + if (ret != sizeof(val)) > + return false; > + > + return true; > +} -- Thiago