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Subject[PATCH v7 3.2-rc2 30/30] x86: skip singlestep where possible

Check and skip singlestepping underlying instructions where possible.

For now handles single byte as well as few multibyte nop instructions.
However can be extended to other instructions too.

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
arch/x86/kernel/uprobes.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 44 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 3f0eb4e..f59053f 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -602,3 +602,47 @@ void abort_xol(struct pt_regs *regs, struct uprobe *uprobe)
handle_riprel_post_xol(uprobe, regs, NULL);
set_instruction_pointer(regs, utask->vaddr);
}
+
+/*
+ * Skip these instructions:
+ *
+ * 0f 19 90 90 90 90 90 nopl -0x6f6f6f70(%rax)
+ * 0f 1f 00 nopl (%rax)
+ * 0f 1f 40 00 nopl 0x0(%rax)
+ * 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
+ * 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
+ * 0f 1f 84 00 00 00 00 nopl 0x0(%rax,%rax,1)
+ * 66 0f 1f 44 00 00 00 nopw 0x0(%rax,%rax,1)
+ * 66 0f 1f 84 00 00 00 nopw 0x0(%rax,%rax,1)
+ * 66 87 c0 xchg %eax,%eax
+ * 66 90 nop
+ * 87 c0 xchg %eax,%eax
+ * 90 nop
+ */
+
+bool can_skip_xol(struct pt_regs *regs, struct uprobe *u)
+{
+ int i;
+
+ for (i = 0; i < MAX_UINSN_BYTES; i++) {
+ if ((u->insn[i] == 0x66))
+ continue;
+
+ if (u->insn[i] == 0x90)
+ return true;
+
+ if ((u->insn[i] == 0x0f) && (u->insn[i+1] == 0x1f))
+ return true;
+
+ if ((u->insn[i] == 0x0f) && (u->insn[i+1] == 0x19))
+ return true;
+
+ if ((u->insn[i] == 0x87) && (u->insn[i+1] == 0xc0))
+ return true;
+
+ break;
+ }
+
+ u->flags &= ~UPROBES_SKIP_SSTEP;
+ return false;
+}


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