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Date: Thu, 23 Jul 2015 16:40:14 -0700 From: Andy Lutomirski <luto@...capital.net> To: Kees Cook <keescook@...omium.org> Cc: Willy Tarreau <w@....eu>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Steven Rostedt <rostedt@...dmis.org>, "security@...nel.org" <security@...nel.org>, X86 ML <x86@...nel.org>, Borislav Petkov <bp@...en8.de>, Sasha Levin <sasha.levin@...cle.com>, LKML <linux-kernel@...r.kernel.org>, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, Boris Ostrovsky <boris.ostrovsky@...cle.com>, Andrew Cooper <andrew.cooper3@...rix.com>, Jan Beulich <jbeulich@...e.com>, xen-devel <xen-devel@...ts.xen.org> Subject: Re: [PATCH v3 2/3] x86/ldt: Make modify_ldt optional On Thu, Jul 23, 2015 at 4:36 PM, Kees Cook <keescook@...omium.org> wrote: > On Thu, Jul 23, 2015 at 3:24 AM, Willy Tarreau <w@....eu> wrote: >> #ifdef CONFIG_SMP >> static void flush_ldt(void *current_mm) >> { >> @@ -254,6 +260,9 @@ asmlinkage int sys_modify_ldt(int func, void __user *ptr, >> { >> int ret = -ENOSYS; >> >> + if (!sysctl_modify_ldt) >> + return ret; >> + >> switch (func) { >> case 0: >> ret = read_ldt(ptr, bytecount); >> diff --git a/kernel/sysctl.c b/kernel/sysctl.c >> index 2082b1a..60270c6 100644 >> --- a/kernel/sysctl.c >> +++ b/kernel/sysctl.c >> @@ -111,6 +111,9 @@ extern int sysctl_nr_open_min, sysctl_nr_open_max; >> #ifndef CONFIG_MMU >> extern int sysctl_nr_trim_pages; >> #endif >> +#ifdef CONFIG_X86 >> +extern int sysctl_modify_ldt; >> +#endif >> >> /* Constants used for minimum and maximum */ >> #ifdef CONFIG_LOCKUP_DETECTOR >> @@ -962,6 +965,13 @@ static struct ctl_table kern_table[] = { >> .mode = 0644, >> .proc_handler = proc_dointvec, >> }, >> + { >> + .procname = "modify_ldt", >> + .data = &sysctl_modify_ldt, >> + .maxlen = sizeof(int), >> + .mode = 0644, >> + .proc_handler = proc_dointvec, >> + }, >> #endif >> #if defined(CONFIG_MMU) >> { > > I've been pondering something like this that is even MORE generic, for > any syscall. Something like a "syscalls" directory under > /proc/sys/kernel, with 1 entry per syscall. "0" is "available", "1" is > disabled, and "-1" disabled until next boot. > It might want to be /proc/sys/kernel/syscalls/[abi]/[name], possibly with more than just those options. We might want "disabled, returns ENOSYS", "disabled, returns EPERM", and a lock bit. On x86 at least, the implementation's easy -- we can just poke the syscall table. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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