Messages in this thread Patch in this message | | | Date | Wed, 28 Oct 2020 17:14:44 -0400 | From | Steven Rostedt <> | Subject | Re: [RFC][PATCH 1/2 v2] ftrace/x86: Allow for arguments to be passed in to REGS by default |
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On Wed, 28 Oct 2020 16:36:26 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
> Here's a proof of concept patch. It passes all the kprobe self tests in > the ftracetest suite. This is just a proof of concept, and I already > know of a couple of subtle bugs that are easy to fix. But this shows > the general idea.
And this works for live patching as well (the below patch passed the live patching test).
To make sure this really worked, I made the regular trampoline put RIP into the R15 location, and live patching used that.
I'm going to start working on getting rid of FL_SAVE_REGS, by first changing the regs parameter to struct ftrace_regs * type, and having all regs users use ftrace_regs_get_regs(), that will return NULL if it's not full regs (at least for x86), this way we can keep the current regs (if kprobes *really* needs it). But then having other accesses for this. And this way, live patching will no longer need a full regs to work.
Then by default we can have all callbacks have access to the stack and arguments!
-- Steve
diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h index 1fde1ab6559e..de3bf7ce1c5d 100644 --- a/arch/x86/include/asm/livepatch.h +++ b/arch/x86/include/asm/livepatch.h @@ -14,7 +14,7 @@ static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip) { - regs->ip = ip; + regs->r15 = ip; } #endif /* _ASM_X86_LIVEPATCH_H */ diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S index f8833fe0ff44..aad647500818 100644 --- a/arch/x86/kernel/ftrace_64.S +++ b/arch/x86/kernel/ftrace_64.S @@ -148,6 +148,11 @@ SYM_INNER_LABEL(ftrace_caller_op_ptr, SYM_L_GLOBAL) /* Load the ftrace_ops into the 3rd parameter */ movq function_trace_op(%rip), %rdx + /* put RIP into R15 to test this */ + movq RIP(%rsp), %rcx + movq %rcx, R15(%rsp) + movq $0, RIP(%rsp) + /* regs go into 4th parameter */ leaq (%rsp), %rcx @@ -158,7 +163,7 @@ SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) call ftrace_stub /* Handlers can change the RIP */ - movq RIP(%rsp), %rax + movq R15(%rsp), %rax movq %rax, MCOUNT_REG_SIZE(%rsp) restore_mcount_regs diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c index c3a5b2675397..3374d53a747a 100644 --- a/arch/x86/kernel/kprobes/ftrace.c +++ b/arch/x86/kernel/kprobes/ftrace.c @@ -22,6 +22,7 @@ static void arch_ftrace_fill_regs(struct pt_regs *regs, struct pt_regs *ftrace_regs) { *regs = *ftrace_regs; + regs->ip = regs->r15; local_save_flags(regs->flags); regs->cs = __KERNEL_CS; } @@ -30,6 +31,7 @@ static void arch_regs_fill_ftrace(struct pt_regs *ftrace_regs, struct pt_regs *regs) { *ftrace_regs = *regs; + ftrace_regs->r15 = regs->ip; } /* Ftrace callback handler for kprobes -- called under preepmt disabed */ diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c index 6c0164d24bbd..87ecdf486ca3 100644 --- a/kernel/livepatch/patch.c +++ b/kernel/livepatch/patch.c @@ -199,8 +199,10 @@ static int klp_patch_func(struct klp_func *func) return -ENOMEM; ops->fops.func = klp_ftrace_handler; - ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS | - FTRACE_OPS_FL_DYNAMIC | + ops->fops.flags = FTRACE_OPS_FL_DYNAMIC | +#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS + FTRACE_OPS_FL_SAVE_REGS | +#endif FTRACE_OPS_FL_IPMODIFY | FTRACE_OPS_FL_PERMANENT;
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