Messages in this thread | | | Date | Tue, 15 Apr 2008 00:29:18 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 2/3] x86: Implement prctl PR_GET_TSC and PR_SET_TSC |
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On Fri, 11 Apr 2008 18:55:58 +0200 (CEST) Erik Bosman <ebn310@few.vu.nl> wrote:
> > x86: Implement prctl PR_GET_TSC and PR_SET_TSC > > This patch adds a configure option CONFIG_DISABLE_TSC > (off by default) for the x86 platform to enable the > PR_GET_TSC and PR_SET_TSC commands. These control the > ability to use the timestamp counter from userspace > (the RDTSC instruction.) > > This patch uses code earlier used to disable the > timestamp counter for the SECCOMP framework. It used > to disable the RDTSC on 32 bit kernels, but allow it > on x86_64. This patch makes SECCOMP disable the > timestamp counter whenever CONFIG_DISABLE_TSC is > enabled. > > ... > > +config DISABLE_TSC > + def_bool n > + prompt "Make availability of the RDTSC instruction configurable" > + depends on (X86_32 || X86_64) && EXPERIMENTAL > + help > + While the RDTSC instruction allows for very precise time > + measurements, it is also a source for non-determinism > + during the execution of a process which can be a problem in some > + security contexts. This option adds prctl commands to configure > + and test the availability of the RDTSC instruction on a > + per-process basis. Choosing this option may cause a small > + performance hit during context switching. > + > + If unsure, say N. > + > config SECCOMP > def_bool y > prompt "Enable seccomp to safely compute untrusted bytecode" > diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c > index 6496344..e6a861f 100644 > --- a/arch/x86/kernel/process_32.c > +++ b/arch/x86/kernel/process_32.c > @@ -36,6 +36,7 @@ > #include <linux/personality.h> > #include <linux/tick.h> > #include <linux/percpu.h> > +#include <linux/prctl.h> > > #include <asm/uaccess.h> > #include <asm/pgtable.h> > @@ -528,11 +529,12 @@ start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp) > } > EXPORT_SYMBOL_GPL(start_thread); > > -#ifdef CONFIG_SECCOMP > +#ifdef CONFIG_DISABLE_TSC > static void hard_disable_TSC(void) > { > write_cr4(read_cr4() | X86_CR4_TSD); > }
Won't this break this build if CONFIG_DISABLE_TSC=n and CONFIG_SECCOMP=y?
The prctl.h and sys.c parts look OK to me. I'll consider this a git-x86 patch.
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