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Wed, 24 Jan 2024 22:29:35 -0800 (PST) Received: from debug.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id t19-20020a056a00139300b006dd870b51b8sm3201139pfg.126.2024.01.24.22.29.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Jan 2024 22:29:34 -0800 (PST) From: debug@rivosinc.com To: rick.p.edgecombe@intel.com, broonie@kernel.org, Szabolcs.Nagy@arm.com, kito.cheng@sifive.com, keescook@chromium.org, ajones@ventanamicro.com, paul.walmsley@sifive.com, palmer@dabbelt.com, conor.dooley@microchip.com, cleger@rivosinc.com, atishp@atishpatra.org, alex@ghiti.fr, bjorn@rivosinc.com, alexghiti@rivosinc.com Cc: corbet@lwn.net, aou@eecs.berkeley.edu, oleg@redhat.com, akpm@linux-foundation.org, arnd@arndb.de, ebiederm@xmission.com, shuah@kernel.org, brauner@kernel.org, debug@rivosinc.com, guoren@kernel.org, samitolvanen@google.com, evan@rivosinc.com, xiao.w.wang@intel.com, apatel@ventanamicro.com, mchitale@ventanamicro.com, waylingii@gmail.com, greentime.hu@sifive.com, heiko@sntech.de, jszhang@kernel.org, shikemeng@huaweicloud.com, david@redhat.com, charlie@rivosinc.com, panqinglin2020@iscas.ac.cn, willy@infradead.org, vincent.chen@sifive.com, andy.chiu@sifive.com, gerg@kernel.org, jeeheng.sia@starfivetech.com, mason.huo@starfivetech.com, ancientmodern4@gmail.com, mathis.salmen@matsal.de, cuiyunhui@bytedance.com, bhe@redhat.com, chenjiahao16@huawei.com, ruscur@russell.cc, bgray@linux.ibm.com, alx@kernel.org, baruch@tkos.co.il, zhangqing@loongson.cn, catalin.marinas@arm.com, revest@chromium.org, josh@joshtriplett.org, joey.gouly@arm.com, shr@devkernel.io, omosnace@redhat.com, ojeda@kernel.org, jhubbard@nvidia.com, linux-doc@vger.kernel.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [RFC PATCH v1 11/28] riscv: Implementing "PROT_SHADOWSTACK" on riscv Date: Wed, 24 Jan 2024 22:21:36 -0800 Message-ID: <20240125062739.1339782-12-debug@rivosinc.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240125062739.1339782-1-debug@rivosinc.com> References: <20240125062739.1339782-1-debug@rivosinc.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Deepak Gupta This patch implements new risc-v specific protection flag `PROT_SHADOWSTACK` (only for kernel) on riscv. `PROT_SHADOWSTACK` protection flag is only limited to kernel and not exposed to userspace. Shadow stack is a security construct to prevent against ROP a= ttacks. `map_shadow_stack` is a new syscall to manufacture shadow stack. In order t= o avoid multiple methods to create shadow stack, `PROT_SHADOWSTACK` is not allowed = for user space `mmap` call. `mprotect` wouldn't allow because `arch_validate_prot` a= lready takes care of this for risc-v. `arch_calc_vm_prot_bits` is implemented on risc-v to return VM_SHADOW_STACK= (alias for VM_WRITE) if PROT_SHADOWSTACK is supplied (such as call to `do_mmap` wi= ll) and underlying CPU supports shadow stack. `PROT_WRITE` will be converted to `VM= _READ | `VM_WRITE` so that existing case where `PROT_WRITE` is specified keep worki= ng but don't collide with `VM_WRITE` only encoding which now denotes a shadow stac= k. risc-v `mmap` wrapper enforces if PROT_WRITE is specified and PROT_READ is = left out then PROT_READ is enforced. Earlier `protection_map[VM_WRITE]` used to pick read-write (and copy on wri= te) PTE encodings. Now all non-shadow stack writeable mappings will pick `protectio= n_map[VM_WRITE | VM_READ] PTE encodings. `protection[VM_WRITE]` are programmed to pick PAG= E_SHADOWSTACK PTE encordings. Signed-off-by: Deepak Gupta --- arch/riscv/include/asm/mman.h | 17 +++++++++++++++++ arch/riscv/include/asm/pgtable.h | 1 + arch/riscv/kernel/sys_riscv.c | 19 +++++++++++++++++++ arch/riscv/mm/init.c | 2 +- 4 files changed, 38 insertions(+), 1 deletion(-) diff --git a/arch/riscv/include/asm/mman.h b/arch/riscv/include/asm/mman.h index 4902d837e93c..bc09a9c0e81f 100644 --- a/arch/riscv/include/asm/mman.h +++ b/arch/riscv/include/asm/mman.h @@ -22,4 +22,21 @@ */ #define PROT_SHADOWSTACK 0x40 =20 +static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot, + unsigned long pkey __always_unused) +{ + unsigned long ret =3D 0; + + if (cpu_supports_shadow_stack()) + ret =3D (prot & PROT_SHADOWSTACK) ? VM_SHADOW_STACK : 0; + /* + * If PROT_WRITE was specified, force it to VM_READ | VM_WRITE. + * Only VM_WRITE means shadow stack. + */ + if (prot & PROT_WRITE) + ret =3D (VM_READ | VM_WRITE); + return ret; +} +#define arch_calc_vm_prot_bits(prot, pkey) arch_calc_vm_prot_bits(prot, pk= ey) + #endif /* ! __ASM_MMAN_H__ */ diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgta= ble.h index 294044429e8e..54a8dde29504 100644 --- a/arch/riscv/include/asm/pgtable.h +++ b/arch/riscv/include/asm/pgtable.h @@ -184,6 +184,7 @@ extern struct pt_alloc_ops pt_ops __initdata; #define PAGE_READ_EXEC __pgprot(_PAGE_BASE | _PAGE_READ | _PAGE_EXEC) #define PAGE_WRITE_EXEC __pgprot(_PAGE_BASE | _PAGE_READ | \ _PAGE_EXEC | _PAGE_WRITE) +#define PAGE_SHADOWSTACK __pgprot(_PAGE_BASE | _PAGE_WRITE) =20 #define PAGE_COPY PAGE_READ #define PAGE_COPY_EXEC PAGE_READ_EXEC diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c index a2ca5b7756a5..2a7cf28a6fe0 100644 --- a/arch/riscv/kernel/sys_riscv.c +++ b/arch/riscv/kernel/sys_riscv.c @@ -16,6 +16,7 @@ #include #include #include +#include =20 static long riscv_sys_mmap(unsigned long addr, unsigned long len, unsigned long prot, unsigned long flags, @@ -25,6 +26,24 @@ static long riscv_sys_mmap(unsigned long addr, unsigned = long len, if (unlikely(offset & (~PAGE_MASK >> page_shift_offset))) return -EINVAL; =20 + /* + * If only 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_WRI= TE | 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 |=3D PROT_READ; + + /* + * PROT_SHADOWSTACK is a kernel only protection flag on risc-v. + * mmap doesn't expect PROT_SHADOWSTACK to be set by user space. + * User space can rely on `map_shadow_stack` syscall to create + * shadow stack pages. + */ + if (unlikely(prot & PROT_SHADOWSTACK)) + return -EINVAL; + return ksys_mmap_pgoff(addr, len, prot, flags, fd, offset >> (PAGE_SHIFT - page_shift_offset)); } diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c index 2e011cbddf3a..f71c2d2c6cbf 100644 --- a/arch/riscv/mm/init.c +++ b/arch/riscv/mm/init.c @@ -296,7 +296,7 @@ pgd_t early_pg_dir[PTRS_PER_PGD] __initdata __aligned(P= AGE_SIZE); static const pgprot_t protection_map[16] =3D { [VM_NONE] =3D PAGE_NONE, [VM_READ] =3D PAGE_READ, - [VM_WRITE] =3D PAGE_COPY, + [VM_WRITE] =3D PAGE_SHADOWSTACK, [VM_WRITE | VM_READ] =3D PAGE_COPY, [VM_EXEC] =3D PAGE_EXEC, [VM_EXEC | VM_READ] =3D PAGE_READ_EXEC, --=20 2.43.0