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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id k20sm11602048pgn.62.2020.04.06.16.16.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Apr 2020 16:16:14 -0700 (PDT) From: Kees Cook To: Thomas Gleixner Cc: Kees Cook , Elena Reshetova , x86@kernel.org, Andy Lutomirski , Peter Zijlstra , Catalin Marinas , Will Deacon , Mark Rutland , Alexander Potapenko , Ard Biesheuvel , Jann Horn , kernel-hardening@lists.openwall.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v3 5/5] arm64: entry: Enable random_kstack_offset support Date: Mon, 6 Apr 2020 16:16:06 -0700 Message-Id: <20200406231606.37619-6-keescook@chromium.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200406231606.37619-1-keescook@chromium.org> References: <20200406231606.37619-1-keescook@chromium.org> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable 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: Allow for a randomized stack offset on a per-syscall basis, with roughly 5 bits of entropy. In order to avoid unconditional stack canaries on syscall entry, also downgrade from -fstack-protector-strong to -fstack-protector to avoid triggering checks due to alloca(). Examining the resulting syscall.o, sees no changes in canary coverage (none before, none now). Signed-off-by: Kees Cook --- arch/arm64/Kconfig | 1 + arch/arm64/kernel/Makefile | 4 ++++ arch/arm64/kernel/syscall.c | 10 ++++++++++ 3 files changed, 15 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 0b30e884e088..4d5aa4959f72 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -127,6 +127,7 @@ config ARM64 select HAVE_ARCH_MMAP_RND_BITS select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT select HAVE_ARCH_PREL32_RELOCATIONS + select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET select HAVE_ARCH_SECCOMP_FILTER select HAVE_ARCH_STACKLEAK select HAVE_ARCH_THREAD_STRUCT_WHITELIST diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index fc6488660f64..b89005f125d6 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -11,6 +11,10 @@ CFLAGS_REMOVE_ftrace.o =3D $(CC_FLAGS_FTRACE) CFLAGS_REMOVE_insn.o =3D $(CC_FLAGS_FTRACE) CFLAGS_REMOVE_return_address.o =3D $(CC_FLAGS_FTRACE) =20 +# Downgrade to -fstack-protector to avoid triggering unneeded stack cana= ry +# checks due to randomize_kstack_offset. +CFLAGS_syscall.o +=3D $(subst -fstack-protector-strong,-fstack-protector= ,$(filter -fstack-protector-strong,$(KBUILD_CFLAGS))) + # Object file lists. obj-y :=3D debug-monitors.o entry.o irq.o fpsimd.o \ entry-common.o entry-fpsimd.o process.o ptrace.o \ diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c index a12c0c88d345..238dbd753b44 100644 --- a/arch/arm64/kernel/syscall.c +++ b/arch/arm64/kernel/syscall.c @@ -5,6 +5,7 @@ #include #include #include +#include #include =20 #include @@ -42,6 +43,8 @@ static void invoke_syscall(struct pt_regs *regs, unsign= ed int scno, { long ret; =20 + add_random_kstack_offset(); + if (scno < sc_nr) { syscall_fn_t syscall_fn; syscall_fn =3D syscall_table[array_index_nospec(scno, sc_nr)]; @@ -51,6 +54,13 @@ static void invoke_syscall(struct pt_regs *regs, unsig= ned int scno, } =20 regs->regs[0] =3D ret; + + /* + * Since the compiler chooses a 4 bit alignment for the stack, + * let's save one additional bit (9 total), which gets us up + * near 5 bits of entropy. + */ + choose_random_kstack_offset(get_random_int() & 0x1FF); } =20 static inline bool has_syscall_work(unsigned long flags) --=20 2.20.1