Messages in this thread | | | From | "Reshetova, Elena" <> | Subject | RE: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall | Date | Fri, 12 Apr 2019 05:36:18 +0000 |
| |
> On Wed, Apr 10, 2019 at 3:24 AM Reshetova, Elena > <elena.reshetova@intel.com> wrote: > > > > > > > > > On Mon, Apr 08, 2019 at 09:13:58AM +0300, Elena Reshetova wrote: > > > > > > diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c > > > > > > index 7bc105f47d21..38ddc213a5e9 100644 > > > > > > --- a/arch/x86/entry/common.c > > > > > > +++ b/arch/x86/entry/common.c > > > > > > @@ -35,6 +35,12 @@ > > > > > > #define CREATE_TRACE_POINTS > > > > > > #include <trace/events/syscalls.h> > > > > > > > > > > > > +#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET > > > > > > +#include <linux/random.h> > > > > > > + > > > > > > +void *alloca(size_t size); > > > > > > +#endif > > > > > > + > > > > > > #ifdef CONFIG_CONTEXT_TRACKING > > > > > > /* Called on entry from user mode with IRQs off. */ > > > > > > __visible inline void enter_from_user_mode(void) > > > > > > @@ -273,6 +279,13 @@ __visible void do_syscall_64(unsigned long nr, > struct > > > > pt_regs *regs) > > > > > > { > > > > > > struct thread_info *ti; > > > > > > > > > > > > +#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET > > > > > > + size_t offset = ((size_t)prandom_u32()) % 256; > > > > > > + char *ptr = alloca(offset); > > > > > > + > > > > > > + asm volatile("":"=m"(*ptr)); > > > > > > +#endif > > > > > > + > > > > > > enter_from_user_mode(); > > > > > > local_irq_enable(); > > > > > > ti = current_thread_info(); > > > > > > > > > > Would it make sense to also do this for the compat syscalls > > > > > (do_fast_syscall_32, do_int80_syscall_32)? > > > > > > > > Could someone please include the full patch, with justification and > > > > performance impact analysis etc.? Can only find the code part of the > > > > thread on lkml, which leaves out this context. > > > > > > > > > > Sorry, this is very weird, I cannot find it either from lkml, but it was sent there > > > to begin with (and as visible from reply-to headers). > > > > > > Do you want me to resent original version or with "do_fast_syscall_32, > > > do_int80_syscall_32" additions (I am finishing testing them now). > > > > I will resend the original x86_64 now since this is the one I tested and > > measured properly. The 32 bit changes seem to work fine inside my 32 bit VM, > > but since I don't have any real 32 bit HW, I am hesitant to send them out without > > real HW testing and measuring. > > > > This is the asm code for 32 bits (note it requires __builtin_alloca definition and not > just alloca, > > so I will change the 64 bit version to use it also): > > > > #ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET > > size_t offset = ((size_t)prandom_u32()) % 256; > > 0xc10025b6 call 0xc146f7d0 <prandom_u32> > > 0xc10025bb movzbl %al,%eax > > char *ptr = __builtin_alloca(offset); > > 0xc10025be add $0x12,%eax > > 0xc10025c1 and $0x1fc,%eax > > 0xc10025c6 sub %eax,%esp > > 0xc10025c8 lea 0x27(%esp),%eax > > 0xc10025cc and $0xfffffff0,%eax > > > > Also, the result is 47 different random offsets produced, > > which is slightly better than 33 offsets for x86_64. > > > > I would suggest that you macro-ify this thing: > > #ifdef WHATEVER > #define add_random_stack_offset() do { void *addr = ... } while (0) > #else > #define add_random_stack_offset() do {} while (0) > #endif > > since you'll end up with more than one call site.
Sure, will do. So, you are ok for this to be also called from do_fast_syscall_32 and do_int80_syscall_32? I can send the resulting patch, just cannot test on any real 32 bit HW, only VM.
Best Regards, Elena.
| |