Messages in this thread | | | Date | Tue, 13 Mar 2012 06:20:16 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] uprobes/core: handle breakpoint and signal step exception. |
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* Ingo Molnar <mingo@elte.hu> wrote:
> > * Srikar Dronamraju <srikar@linux.vnet.ibm.com> wrote: > > > * Ingo Molnar <mingo@elte.hu> [2012-03-08 14:48:09]: > > > > > > > > * Srikar Dronamraju <srikar@linux.vnet.ibm.com> wrote: > > > > > > > @@ -233,9 +233,11 @@ static inline void __user *arch_compat_alloc_user_space(long len) > > > > > > > > if (test_thread_flag(TIF_IA32)) { > > > > sp = task_pt_regs(current)->sp; > > > > +#ifdef CONFIG_X86_64 > > > > } else { > > > > /* -128 for the x32 ABI redzone */ > > > > sp = __this_cpu_read(old_rsp) - 128; > > > > +#endif > > > > } > > > > > > > > return (void __user *)round_down(sp - len, 16); > > > > > > So 'sp' is undefined if that TIF check fails? > > > > > > Also, on a 32-bit kernel the TIF check probably fails all the > > > time, because we don't set TIF_IA32 (and don't know that flag). > > > > > > > > It would probably be better to make the whole helper inline > > > #ifdef 64-bit, it does not look very useful on 32-bit. > > > > > > > arch_compat_alloc_user_space gets called from compat_alloc_user_space > > which is arch agnostic and exported too. > > > > So I will change this to > > > > void __user *arch_compat_alloc_user_space(long len) > > { > > if (is_ia32_compat_task(current)) > > sp = task_pt_regs(current)->sp; > > #ifdef CONFIG_X86_64 > > else > > /* -128 for the x32 ABI redzone */ > > sp = __this_cpu_read(old_rsp) - 128; > > #endif > > > > return (void __user *)round_down(sp - len, 16); > > } > > > > where is_ia32_compat_task() is the new macro that you > > suggested we put in compat.h which would return true if the > > task is 32 bit emulated on x86_64 or running on i386 machine. > > > > Hence we can avoid the case where sp is not set. > > Ok - looks good at first glance.
It does not look good on a second glance though, once I checked your latest patches.
arch_compat_alloc_user_space() is arch agnostic on *CONFIG_COMPAT=y* kernels.
It's generally not available on 32-bit builds - CONFIG_COMPAT is a facility to provide 32-bit syscall compatibility on 64-bit kernels. Such a facility is not needed on 32-bit kernels.
So providing this:
> void __user *arch_compat_alloc_user_space(long len) > { > if (is_ia32_compat_task(current)) > sp = task_pt_regs(current)->sp;
on 32-bit systems makes little sense.
So ... instead of adding is_compat_task() to compat.h it would be better to add it to another x86 header (processor.h might be good but I have not checked very hard) and maybe name it is_32bit_task() or so, to make sure there's no confusion with CONFIG_COMPAT=y methods.
I.e. you could drop this patch altogether:
x86/trivial: Fix 'old_rsp' undefined build failure when including asm/compat.h
And rework the is_ia32_compat_task() patch to use another header and to use the is_32bit_task() name. Also, you should double check whether the x32 execution model needs special consideration as well:
#define TIF_IA32 17 /* IA32 compatibility process */ #define TIF_X32 30 /* 32-bit native x86-64 binary */
otherwise uprobe will not work with x32 tasks properly.
Thanks,
Ingo
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