[PATCH 3/4] Add condition code checking to SWP emulation handler.

Leif Lindholm leif.lindholm at arm.com
Thu Dec 8 12:32:06 EST 2011

This patch fixes two separate issues with the SWP emulation handler:
1: Certain processors implementing ARMv7-A can (legally) take an
   undef exception even when the condition code would have meant that
   the instruction should not have been executed.
2: Opcodes with all flags set (condition code = 0xf) have been reused
   in recent, and not-so-recent, versions of the ARM architecture to
   implement unconditional extensions to the instruction set. The
   existing code would still have processed any undefs triggered by
   executing an opcode with such a value.

This patch uses the new generic ARM instruction set condition code
checks to implement proper handling of these situations.

Signed-off-by: Leif Lindholm <leif.lindholm at arm.com>
 arch/arm/kernel/swp_emulate.c |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/arch/arm/kernel/swp_emulate.c b/arch/arm/kernel/swp_emulate.c
index 5f452f8..6a5210e 100644
--- a/arch/arm/kernel/swp_emulate.c
+++ b/arch/arm/kernel/swp_emulate.c
@@ -25,6 +25,7 @@
 #include <linux/syscalls.h>
 #include <linux/perf_event.h>
+#include <asm/opcodes.h>
 #include <asm/traps.h>
 #include <asm/uaccess.h>
@@ -185,6 +186,17 @@ static int swp_handler(struct pt_regs *regs, unsigned int instr)
 	perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
+	res = arm_check_condition(instr, regs->ARM_cpsr);
+	switch (res) {
+		/* Condition failed - return to next instruction */
+		regs->ARM_pc += 4;
+		return 0;
+		/* If unconditional encoding - not a SWP, undef */
+		return -EFAULT;
+	}
 	if (current->pid != previous_pid) {
 		pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
 			 current->comm, (unsigned long)current->pid);

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