ARM: kprobes: Add emulation of SBFX, UBFX, BFI and BFC instructions

These bit field manipulation instructions occur several thousand
times in an ARMv7 kernel.

Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>

1 files changed, 42 insertions, 0 deletions

diff --git a/arch/arm/kernel/kprobes-decode.c b/arch/arm/kernel/kprobes-decode.c
index a063f152d9b3..6bed8b089af0 100644
--- a/arch/arm/kernel/kprobes-decode.c
+++ b/arch/arm/kernel/kprobes-decode.c
@@ -672,6 +672,19 @@ emulate_rd12_modify(struct kprobe *p, struct pt_regs *regs)
         regs->uregs[rd] = insnslot_1arg_rflags(rdv, regs->ARM_cpsr, i_fn);
 }
 
+static void __kprobes
+emulate_rd12rn0_modify(struct kprobe *p, struct pt_regs *regs)
+{
+        insn_2arg_fn_t *i_fn = (insn_2arg_fn_t *)&p->ainsn.insn[0];
+        kprobe_opcode_t insn = p->opcode;
+        int rd = (insn >> 12) & 0xf;
+        int rn = insn & 0xf;
+        long rdv = regs->uregs[rd];
+        long rnv = regs->uregs[rn];
+
+        regs->uregs[rd] = insnslot_2arg_rflags(rdv, rnv, regs->ARM_cpsr, i_fn);
+}
+
 static void __kprobes emulate_rd12rm0(struct kprobe *p, struct pt_regs *regs)
 {
         insn_1arg_fn_t *i_fn = (insn_1arg_fn_t *)&p->ainsn.insn[0];
@@ -870,6 +883,20 @@ prep_emulate_rd12_modify(kprobe_opcode_t insn, struct arch_specific_insn *asi)
 }
 
 static enum kprobe_insn __kprobes
+prep_emulate_rd12rn0_modify(kprobe_opcode_t insn,
+                            struct arch_specific_insn *asi)
+{
+        if (is_r15(insn, 12))
+                return INSN_REJECTED;   /* Rd is PC */
+
+        insn &= 0xffff0ff0;     /* Rd = r0 */
+        insn |= 0x00000001;     /* Rn = r1 */
+        asi->insn[0] = insn;
+        asi->insn_handler = emulate_rd12rn0_modify;
+        return INSN_GOOD;
+}
+
+static enum kprobe_insn __kprobes
 prep_emulate_rd12rm0(kprobe_opcode_t insn, struct arch_specific_insn *asi)
 {
         if (is_r15(insn, 12))
@@ -1396,6 +1423,21 @@ space_cccc_0111__1(kprobe_opcode_t insn, struct arch_specific_insn *asi)
         if ((insn & 0x0ff000d0) == 0x075000d0)
                 return prep_emulate_rd16rn12rs8rm0_wflags(insn, asi);
 
+        /* SBFX   : cccc 0111 101x xxxx xxxx xxxx x101 xxxx :  */
+        /* UBFX   : cccc 0111 111x xxxx xxxx xxxx x101 xxxx :  */
+        if ((insn & 0x0fa00070) == 0x07a00050)
+                return prep_emulate_rd12rm0(insn, asi);
+
+        /* BFI    : cccc 0111 110x xxxx xxxx xxxx x001 xxxx :  */
+        /* BFC    : cccc 0111 110x xxxx xxxx xxxx x001 1111 :  */
+        if ((insn & 0x0fe00070) == 0x07c00010) {
+
+                if ((insn & 0x0000000f) == 0x0000000f)
+                        return prep_emulate_rd12_modify(insn, asi);
+                else
+                        return prep_emulate_rd12rn0_modify(insn, asi);
+        }
+
         return INSN_REJECTED;
 }