From: Will Deacon <will@kernel.org>
To: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>, Jann Horn <jannh@google.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Peter Zijlstra <peterz@infradead.org>,
Catalin Marinas <catalin.marinas@arm.com>,
x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Alexander Potapenko <glider@google.com>,
linux-arm-kernel@lists.infradead.org,
Andy Lutomirski <luto@kernel.org>,
kernel-hardening@lists.openwall.com, "Perla,
Enrico" <enrico.perla@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Elena Reshetova <elena.reshetova@intel.com>
Subject: Re: [PATCH v2 5/5] arm64: entry: Enable random_kstack_offset support
Date: Mon, 20 Apr 2020 21:54:58 +0100 [thread overview]
Message-ID: <20200420205458.GC29998@willie-the-truck> (raw)
In-Reply-To: <20200324203231.64324-6-keescook@chromium.org>
On Tue, Mar 24, 2020 at 01:32:31PM -0700, Kees Cook wrote:
> Allow for a randomized stack offset on a per-syscall basis, with roughly
> 5 bits of entropy.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> arch/arm64/Kconfig | 1 +
> arch/arm64/kernel/syscall.c | 10 ++++++++++
> 2 files changed, 11 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/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 <linux/errno.h>
> #include <linux/nospec.h>
> #include <linux/ptrace.h>
> +#include <linux/randomize_kstack.h>
> #include <linux/syscalls.h>
>
> #include <asm/daifflags.h>
> @@ -42,6 +43,8 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
> {
> long ret;
>
> + add_random_kstack_offset();
> +
> if (scno < sc_nr) {
> syscall_fn_t syscall_fn;
> syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)];
> @@ -51,6 +54,13 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
> }
>
> regs->regs[0] = 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);
Hmm, this comment doesn't make any sense to me. I mean, I get that 0x1ff
is 9 bits, and that is 4+5 but so what?
Will
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next prev parent reply other threads:[~2020-04-20 20:55 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-24 20:32 [PATCH v2 0/5] Optionally randomize kernel stack offset each syscall Kees Cook
2020-03-24 20:32 ` [PATCH v2 1/5] jump_label: Provide CONFIG-driven build state defaults Kees Cook
2020-03-24 22:06 ` Peter Zijlstra
2020-03-24 20:32 ` [PATCH v2 2/5] init_on_alloc: Unpessimize default-on builds Kees Cook
2020-03-26 15:48 ` Alexander Potapenko
2020-03-24 20:32 ` [PATCH v2 3/5] stack: Optionally randomize kernel stack offset each syscall Kees Cook
2020-03-30 11:25 ` Mark Rutland
2020-03-30 18:18 ` Kees Cook
2020-03-30 18:27 ` Kees Cook
2020-03-24 20:32 ` [PATCH v2 4/5] x86/entry: Enable random_kstack_offset support Kees Cook
2020-03-28 22:26 ` Kees Cook
2020-03-24 20:32 ` [PATCH v2 5/5] arm64: entry: " Kees Cook
2020-03-25 13:21 ` Mark Rutland
2020-03-25 20:22 ` Kees Cook
2020-03-26 11:15 ` Mark Rutland
2020-03-26 16:31 ` Kees Cook
2020-03-30 11:26 ` Mark Rutland
2020-04-20 20:54 ` Will Deacon [this message]
2020-04-20 22:34 ` Kees Cook
2020-04-21 7:02 ` Will Deacon
2020-03-24 21:28 ` [PATCH v2 0/5] Optionally randomize kernel stack offset each syscall Jann Horn
2020-03-24 23:07 ` Kees Cook
2020-03-25 12:15 ` Reshetova, Elena
2020-03-25 20:27 ` Kees Cook
2020-03-25 23:20 ` Jann Horn
2020-03-26 17:18 ` Kees Cook
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