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 <[email protected]>
Acked-by: Kees Cook <[email protected]> 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
