| Message ID | 20210129043507.30488-1-huangpei@loongson.cn (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | MIPS: fix kernel_stack_pointer() | expand |
On Fri, Jan 29, 2021 at 12:35:07PM +0800, Huang Pei wrote: > MIPS always save kernel stack pointer in regs[29] > > Signed-off-by: Huang Pei <huangpei@loongson.cn> > --- > arch/mips/include/asm/ptrace.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/mips/include/asm/ptrace.h b/arch/mips/include/asm/ptrace.h > index 1e76774b36dd..daf3cf244ea9 100644 > --- a/arch/mips/include/asm/ptrace.h > +++ b/arch/mips/include/asm/ptrace.h > @@ -53,7 +53,7 @@ struct pt_regs { > > static inline unsigned long kernel_stack_pointer(struct pt_regs *regs) > { > - return regs->regs[31]; > + return regs->regs[29]; hmm, I'm still wondering where the trick is... looks like this is used for uprobes, so nobody has ever used uprobes or I'm missing something. How did you find that ? Thomas.
On Mon, Feb 01, 2021 at 01:23:52PM +0100, Thomas Bogendoerfer wrote: > On Fri, Jan 29, 2021 at 12:35:07PM +0800, Huang Pei wrote: > > MIPS always save kernel stack pointer in regs[29] > > > > Signed-off-by: Huang Pei <huangpei@loongson.cn> > > --- > > arch/mips/include/asm/ptrace.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/mips/include/asm/ptrace.h b/arch/mips/include/asm/ptrace.h > > index 1e76774b36dd..daf3cf244ea9 100644 > > --- a/arch/mips/include/asm/ptrace.h > > +++ b/arch/mips/include/asm/ptrace.h > > @@ -53,7 +53,7 @@ struct pt_regs { > > > > static inline unsigned long kernel_stack_pointer(struct pt_regs *regs) > > { > > - return regs->regs[31]; > > + return regs->regs[29]; > > hmm, I'm still wondering where the trick is... looks like this is used > for uprobes, so nobody has ever used uprobes or I'm missing something. > > How did you find that ? > > Thomas. > > -- > Crap can work. Given enough thrust pigs will fly, but it's not necessarily a > good idea. [ RFC1925, 2.3 ] Long story for short, +. I think I had fix this bug in 2018, when I backported Uprobe from my 4.4 branch to CentOS 7 3.10. I just knwo it is *not* following MIPS ABI, but I do not know how it destroy the cool function of Kprobe/Uprobe, since the failure in porting eBPF from upstream to 3.10 just leave the fix in 3.10, totally forgotten. +. In 2020, I was told to validate the effect of GNU XHash, and it came to me that using Uprobe to count the number of "strcmp" called in ld.so, so I found this fix again. +. With more work on Kprobe/Kprobe_event/Uprobe, I found it hit only when accessing arguments of Kprobe/Uprobe, so simple counting numbers of probe fired would not trigger it
On Tue, Feb 02, 2021 at 09:32:31AM +0800, Huang Pei wrote: > On Mon, Feb 01, 2021 at 01:23:52PM +0100, Thomas Bogendoerfer wrote: > > On Fri, Jan 29, 2021 at 12:35:07PM +0800, Huang Pei wrote: > > > MIPS always save kernel stack pointer in regs[29] > > > > > > Signed-off-by: Huang Pei <huangpei@loongson.cn> > > > --- > > > arch/mips/include/asm/ptrace.h | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/arch/mips/include/asm/ptrace.h b/arch/mips/include/asm/ptrace.h > > > index 1e76774b36dd..daf3cf244ea9 100644 > > > --- a/arch/mips/include/asm/ptrace.h > > > +++ b/arch/mips/include/asm/ptrace.h > > > @@ -53,7 +53,7 @@ struct pt_regs { > > > > > > static inline unsigned long kernel_stack_pointer(struct pt_regs *regs) > > > { > > > - return regs->regs[31]; > > > + return regs->regs[29]; > > > > hmm, I'm still wondering where the trick is... looks like this is used > > for uprobes, so nobody has ever used uprobes or I'm missing something. > > > > How did you find that ? > > > > Thomas. > > > > -- > > Crap can work. Given enough thrust pigs will fly, but it's not necessarily a > > good idea. [ RFC1925, 2.3 ] > > > Long story for short, > > +. I think I had fix this bug in 2018, when I backported Uprobe from my > 4.4 branch to CentOS 7 3.10. I just knwo it is *not* following MIPS > ABI, but I do not know how it destroy the cool function of > Kprobe/Uprobe, since the failure in porting eBPF from upstream to 3.10 > just leave the fix in 3.10, totally forgotten. > > +. In 2020, I was told to validate the effect of GNU XHash, and it came > to me that using Uprobe to count the number of "strcmp" called in ld.so, > so I found this fix again. > > +. With more work on Kprobe/Kprobe_event/Uprobe, I found it hit only when > accessing arguments of Kprobe/Uprobe, so simple counting numbers of probe > fired would not trigger it Thank you for the explanation, applied to mips-next. Thomas.
diff --git a/arch/mips/include/asm/ptrace.h b/arch/mips/include/asm/ptrace.h index 1e76774b36dd..daf3cf244ea9 100644 --- a/arch/mips/include/asm/ptrace.h +++ b/arch/mips/include/asm/ptrace.h @@ -53,7 +53,7 @@ struct pt_regs { static inline unsigned long kernel_stack_pointer(struct pt_regs *regs) { - return regs->regs[31]; + return regs->regs[29]; } static inline void instruction_pointer_set(struct pt_regs *regs,
MIPS always save kernel stack pointer in regs[29] Signed-off-by: Huang Pei <huangpei@loongson.cn> --- arch/mips/include/asm/ptrace.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)