arm64: Remove stack duplicating code from jprobes

Because the arm64 calling standard allows stacked function arguments to be
anywhere in the stack frame, do not attempt to duplicate the stack frame for
jprobes handler functions.

Documentation changes to describe this issue have been broken out into a
separate patch in order to simultaneously address them in other
architecture(s).

Signed-off-by: David A. Long <dave.long@linaro.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 5 insertions, 26 deletions

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index bf9768588288..c6b0f40620d8 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -41,18 +41,6 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
 static void __kprobes
 post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
 
-static inline unsigned long min_stack_size(unsigned long addr)
-{
-        unsigned long size;
-
-        if (on_irq_stack(addr, raw_smp_processor_id()))
-                size = IRQ_STACK_PTR(raw_smp_processor_id()) - addr;
-        else
-                size = (unsigned long)current_thread_info() + THREAD_START_SP - addr;
-
-        return min(size, FIELD_SIZEOF(struct kprobe_ctlblk, jprobes_stack));
-}
-
 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
 {
         /* prepare insn slot */
@@ -489,20 +477,15 @@ int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 {
         struct jprobe *jp = container_of(p, struct jprobe, kp);
         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
-        long stack_ptr = kernel_stack_pointer(regs);
 
         kcb->jprobe_saved_regs = *regs;
         /*
-         * As Linus pointed out, gcc assumes that the callee
-         * owns the argument space and could overwrite it, e.g.
-         * tailcall optimization. So, to be absolutely safe
-         * we also save and restore enough stack bytes to cover
-         * the argument area.
+         * Since we can't be sure where in the stack frame "stacked"
+         * pass-by-value arguments are stored we just don't try to
+         * duplicate any of the stack. Do not use jprobes on functions that
+         * use more than 64 bytes (after padding each to an 8 byte boundary)
+         * of arguments, or pass individual arguments larger than 16 bytes.
          */
-        kasan_disable_current();
-        memcpy(kcb->jprobes_stack, (void *)stack_ptr,
-               min_stack_size(stack_ptr));
-        kasan_enable_current();
 
         instruction_pointer_set(regs, (unsigned long) jp->entry);
         preempt_disable();
@@ -554,10 +537,6 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
         }
         unpause_graph_tracing();
         *regs = kcb->jprobe_saved_regs;
-        kasan_disable_current();
-        memcpy((void *)stack_addr, kcb->jprobes_stack,
-               min_stack_size(stack_addr));
-        kasan_enable_current();
         preempt_enable_no_resched();
         return 1;
 }