Messages in this thread | | | Date | Tue, 21 Jul 2020 14:47:17 -0700 | From | Kees Cook <> | Subject | Re: [patch V4 10/15] x86/entry: Use generic syscall entry function |
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On Tue, Jul 21, 2020 at 12:57:16PM +0200, Thomas Gleixner wrote: > Replace the syscall entry work handling with the generic version. Provide > the necessary helper inlines to handle the real architecture specific > parts, e.g. ptrace. > > Use a temporary define for idtentry_enter_user which will be cleaned up > seperately. > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Though, notes and a comment below...
> +/* Check that the stack and regs on entry from user mode are sane. */ > +static __always_inline void arch_check_user_regs(struct pt_regs *regs) > +{ > + if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) { > + /* > + * Make sure that the entry code gave us a sensible EFLAGS > + * register. Native because we want to check the actual CPU > + * state, not the interrupt state as imagined by Xen. > + */ > + unsigned long flags = native_save_fl(); > + WARN_ON_ONCE(flags & (X86_EFLAGS_AC | X86_EFLAGS_DF | > + X86_EFLAGS_NT));
push, pop, bit test
> + > + /* We think we came from user mode. Make sure pt_regs agrees. */ > + WARN_ON_ONCE(!user_mode(regs));
memory deref, bit test
> + > + /* > + * All entries from user mode (except #DF) should be on the > + * normal thread stack and should have user pt_regs in the > + * correct location. > + */ > + WARN_ON_ONCE(!on_thread_stack());
per-cpu deref, subtract, test
> + WARN_ON_ONCE(regs != task_pt_regs(current));
memory deref, test
> + } > +}
This doesn't look very expensive, and they certain indicate really bad conditions. Does this need to be behind a CONFIG? (Whatever the answer, we can probably make those changes in a later series -- some of these also look not arch-specific...)
-- Kees Cook
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