From: Kees Cook <keescook@chromium.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
x86@kernel.org, linux-arch@vger.kernel.org,
Will Deacon <will@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
Mark Rutland <mark.rutland@arm.com>,
Keno Fischer <keno@juliacomputing.com>,
Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org,
Gabriel Krisman Bertazi <krisman@collabora.com>
Subject: Re: [patch V4 02/15] entry: Provide generic syscall entry functionality
Date: Tue, 21 Jul 2020 14:38:16 -0700 [thread overview]
Message-ID: <202007211426.B40A7A7BD@keescook> (raw)
In-Reply-To: <20200721110808.455350746@linutronix.de>
On Tue, Jul 21, 2020 at 12:57:08PM +0200, Thomas Gleixner wrote:
> On syscall entry certain work needs to be done:
>
> - Establish state (lockdep, context tracking, tracing)
> - Conditional work (ptrace, seccomp, audit...)
>
> This code is needlessly duplicated and different in all
> architectures.
>
> Provide a generic version based on the x86 implementation which has all the
> RCU and instrumentation bits right.
>
> As interrupt/exception entry from user space needs parts of the same
> functionality, provide a function for this as well.
>
> syscall_enter_from_user_mode() and irqentry_enter_from_user_mode() must be
> called right after the low level ASM entry. The calling code must be
> non-instrumentable. After the functions returns state is correct and the
> subsequent functions can be instrumented.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Kees Cook <keescook@chromium.org>
With one suggestion...
> [...]
> --- /dev/null
> +++ b/kernel/entry/common.c
> @@ -0,0 +1,88 @@
> [...]
> +static inline void syscall_enter_audit(struct pt_regs *regs, long syscall)
> +{
> + if (unlikely(audit_context())) {
> + unsigned long args[6];
> +
> + syscall_get_arguments(current, regs, args);
> + audit_syscall_entry(syscall, args[0], args[1], args[2], args[3]);
> + }
> +}
One thing I noticed while doing syscall entry timings for the kernel
stack base offset randomization was that the stack protector was being
needlessly enabled in certain paths (seccomp, audit) due to seeing a
register array being declared on the stack. As part of that series I
suggested down-grading the stack protector. Since then, Peter's changes
entirely disabled the stack protector on the entry code, which I
grudgingly accept (I'd rather have a way to mark a variable as "ignore
this for stack protector detection", but ... there isn't, so fine.)
> [...]
> --- /dev/null
> +++ b/kernel/entry/Makefile
> @@ -0,0 +1,3 @@
> +# SPDX-License-Identifier: GPL-2.0
> +
> +obj-$(CONFIG_GENERIC_ENTRY) += common.o
But, my point is, let's avoid tripping over this again, and retain the
disabling here:
CFLAGS_common.o += -fno-stack-protector
I can add this again later, but it'd be nice if it was done here to
avoid gaining back the TIF_WORK stack protector overhead penalty (which
we're free of in v5.8 for the first time). ;)
--
Kees Cook
next prev parent reply other threads:[~2020-07-21 21:38 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-21 10:57 [patch V4 00/15] entry, x86, kvm: Generic entry/exit functionality for host and guest Thomas Gleixner
2020-07-21 10:57 ` [patch V4 01/15] seccomp: Provide stub for __secure_computing() Thomas Gleixner
2020-07-21 21:21 ` Kees Cook
2020-07-21 10:57 ` [patch V4 02/15] entry: Provide generic syscall entry functionality Thomas Gleixner
2020-07-21 21:38 ` Kees Cook [this message]
2020-07-22 7:34 ` Thomas Gleixner
2020-07-22 7:54 ` peterz
2020-07-21 10:57 ` [patch V4 03/15] entry: Provide generic syscall exit function Thomas Gleixner
2020-07-27 22:37 ` Andy Lutomirski
2020-07-21 10:57 ` [patch V4 04/15] entry: Provide generic interrupt entry/exit code Thomas Gleixner
2020-07-27 22:39 ` Andy Lutomirski
2020-07-29 12:18 ` Thomas Gleixner
2020-07-21 10:57 ` [patch V4 05/15] entry: Provide infrastructure for work before exiting to guest mode Thomas Gleixner
2020-07-21 10:57 ` [patch V4 06/15] x86/entry: Consolidate check_user_regs() Thomas Gleixner
2020-07-27 22:39 ` Andy Lutomirski
2020-07-21 10:57 ` [patch V4 07/15] x86/entry: Consolidate 32/64 bit syscall entry Thomas Gleixner
2020-07-21 10:57 ` [patch V4 08/15] x86/entry: Move user return notifier out of loop Thomas Gleixner
2020-07-21 10:57 ` [patch V4 09/15] x86/ptrace: Provide pt_regs helper for entry/exit Thomas Gleixner
2020-07-21 10:57 ` [patch V4 10/15] x86/entry: Use generic syscall entry function Thomas Gleixner
2020-07-21 21:47 ` Kees Cook
2020-07-22 18:25 ` Thomas Gleixner
2020-07-21 10:57 ` [patch V4 11/15] x86/entry: Use generic syscall exit functionality Thomas Gleixner
2020-07-21 21:47 ` Kees Cook
2020-07-21 10:57 ` [patch V4 12/15] x86/entry: Cleanup idtentry_entry/exit_user Thomas Gleixner
2020-07-21 21:48 ` Kees Cook
2020-07-21 10:57 ` [patch V4 13/15] x86/entry: Use generic interrupt entry/exit code Thomas Gleixner
2020-07-21 10:57 ` [patch V4 14/15] x86/entry: Cleanup idtentry_enter/exit Thomas Gleixner
2020-07-21 21:48 ` Kees Cook
2020-07-21 10:57 ` [patch V4 15/15] x86/kvm: Use generic exit to guest work function Thomas Gleixner
2020-07-21 20:27 ` Sean Christopherson
2020-07-22 7:40 ` Thomas Gleixner
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