On Tue, Jul 23, 2019 at 07:58:39PM +0200, Andrey Konovalov wrote:
From: Catalin Marinas catalin.marinas@arm.com
It is not desirable to relax the ABI to allow tagged user addresses into the kernel indiscriminately. This patch introduces a prctl() interface for enabling or disabling the tagged ABI with a global sysctl control for preventing applications from enabling the relaxed ABI (meant for testing user-space prctl() return error checking without reconfiguring the kernel). The ABI properties are inherited by threads of the same application and fork()'ed children but cleared on execve(). A Kconfig option allows the overall disabling of the relaxed ABI.
The PR_SET_TAGGED_ADDR_CTRL will be expanded in the future to handle MTE-specific settings like imprecise vs precise exceptions.
Reviewed-by: Kees Cook keescook@chromium.org Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Andrey Konovalov andreyknvl@google.com
Following several discussions on the list and in private, I'm proposing the update below. I can send it as a patch on top of the current series since Will has already queued this.
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From 1b3f57ab0c2c51f8b31c19fb34d270e1f3ee57fe Mon Sep 17 00:00:00 2001
From: Catalin Marinas catalin.marinas@arm.com Date: Fri, 9 Aug 2019 15:09:15 +0100 Subject: [PATCH] fixup! arm64: Introduce prctl() options to control the tagged user addresses ABI
Rename abi.tagged_addr sysctl control to abi.tagged_addr_disabled, defaulting to 0. Only prevent prctl(PR_TAGGED_ADDR_ENABLE)from being called when abi.tagged_addr_disabled==1.
Force unused arg* of the new prctl() to 0.
Signed-off-by: Catalin Marinas catalin.marinas@arm.com --- arch/arm64/kernel/process.c | 17 ++++++++++------- kernel/sys.c | 4 ++++ 2 files changed, 14 insertions(+), 7 deletions(-)
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 76b7c55026aa..03689c0beb34 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -579,17 +579,22 @@ void arch_setup_new_exec(void) /* * Control the relaxed ABI allowing tagged user addresses into the kernel. */ -static unsigned int tagged_addr_prctl_allowed = 1; +static unsigned int tagged_addr_disabled;
long set_tagged_addr_ctrl(unsigned long arg) { - if (!tagged_addr_prctl_allowed) - return -EINVAL; if (is_compat_task()) return -EINVAL; if (arg & ~PR_TAGGED_ADDR_ENABLE) return -EINVAL;
+ /* + * Do not allow the enabling of the tagged address ABI if globally + * disabled via sysctl abi.tagged_addr_disabled. + */ + if (arg & PR_TAGGED_ADDR_ENABLE && tagged_addr_disabled) + return -EINVAL; + update_thread_flag(TIF_TAGGED_ADDR, arg & PR_TAGGED_ADDR_ENABLE);
return 0; @@ -597,8 +602,6 @@ long set_tagged_addr_ctrl(unsigned long arg)
long get_tagged_addr_ctrl(void) { - if (!tagged_addr_prctl_allowed) - return -EINVAL; if (is_compat_task()) return -EINVAL;
@@ -618,9 +621,9 @@ static int one = 1;
static struct ctl_table tagged_addr_sysctl_table[] = { { - .procname = "tagged_addr", + .procname = "tagged_addr_disabled", .mode = 0644, - .data = &tagged_addr_prctl_allowed, + .data = &tagged_addr_disabled, .maxlen = sizeof(int), .proc_handler = proc_dointvec_minmax, .extra1 = &zero, diff --git a/kernel/sys.c b/kernel/sys.c index c6c4d5358bd3..ec48396b4943 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2499,9 +2499,13 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, error = PAC_RESET_KEYS(me, arg2); break; case PR_SET_TAGGED_ADDR_CTRL: + if (arg3 || arg4 || arg5) + return -EINVAL; error = SET_TAGGED_ADDR_CTRL(arg2); break; case PR_GET_TAGGED_ADDR_CTRL: + if (arg2 || arg3 || arg4 || arg5) + return -EINVAL; error = GET_TAGGED_ADDR_CTRL(); break; default: