[PATCH v18 76/80] powerpc: provide APIs for validating and updating DABR

From: Nathan Lynch <ntl@xxxxxxxxx>

A checkpointed task image may specify a value for the DABR (Data
Access Breakpoint Register). The restart code needs to validate this
value before making any changes to the current task.

ptrace_set_debugreg encapsulates the bounds checking and platform
dependencies of programming the DABR. Split this into "validate"
(debugreg_valid) and "update" (debugreg_update) functions, and make
them available for use outside of the ptrace code.

Also ptrace_set_debugreg has extern linkage, but no users outside of
ptrace.c. Make it static.

Signed-off-by: Nathan Lynch <ntl@xxxxxxxxx>
---
arch/powerpc/include/asm/ptrace.h | 7 +++
arch/powerpc/kernel/ptrace.c | 88 +++++++++++++++++++++++++------------
2 files changed, 66 insertions(+), 29 deletions(-)

diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
index 8c34149..c6cb2c6 100644
--- a/arch/powerpc/include/asm/ptrace.h
+++ b/arch/powerpc/include/asm/ptrace.h
@@ -81,6 +81,8 @@ struct pt_regs {

#ifndef __ASSEMBLY__

+#include <linux/types.h>
+
#define instruction_pointer(regs) ((regs)->nip)
#define user_stack_pointer(regs) ((regs)->gpr[1])
#define regs_return_value(regs) ((regs)->gpr[3])
@@ -140,6 +142,11 @@ extern void user_enable_single_step(struct task_struct *);
extern void user_enable_block_step(struct task_struct *);
extern void user_disable_single_step(struct task_struct *);

+/* for reprogramming DABR/DAC during restart of a checkpointed task */
+extern bool debugreg_valid(unsigned long val, unsigned int index);
+extern void debugreg_update(struct task_struct *task, unsigned long val,
+ unsigned int index);
+
#endif /* __ASSEMBLY__ */

#endif /* __KERNEL__ */
diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index ef14988..913ec8f 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -755,22 +755,25 @@ void user_disable_single_step(struct task_struct *task)
clear_tsk_thread_flag(task, TIF_SINGLESTEP);
}

-int ptrace_set_debugreg(struct task_struct *task, unsigned long addr,
- unsigned long data)
+/**
+ * debugreg_valid() - validate the value to be written to a debug register
+ * @val: The prospective contents of the register.
+ * @index: Must be zero.
+ *
+ * Returns true if @val is an acceptable value for the register indicated by
+ * @index, false otherwise.
+ */
+bool debugreg_valid(unsigned long val, unsigned int index)
{
- /* For ppc64 we support one DABR and no IABR's at the moment (ppc64).
- * For embedded processors we support one DAC and no IAC's at the
- * moment.
- */
- if (addr > 0)
- return -EINVAL;
+ /* We support only one debug register for now */
+ if (index != 0)
+ return false;

/* The bottom 3 bits in dabr are flags */
- if ((data & ~0x7UL) >= TASK_SIZE)
- return -EIO;
+ if ((val & ~0x7UL) >= TASK_SIZE)
+ return false;

#ifndef CONFIG_BOOKE
-
/* For processors using DABR (i.e. 970), the bottom 3 bits are flags.
* It was assumed, on previous implementations, that 3 bits were
* passed together with the data address, fitting the design of the
@@ -784,47 +787,74 @@ int ptrace_set_debugreg(struct task_struct *task, unsigned long addr,
*/

/* Ensure breakpoint translation bit is set */
- if (data && !(data & DABR_TRANSLATION))
- return -EIO;
-
- /* Move contents to the DABR register */
- task->thread.dabr = data;
-
-#endif
-#if defined(CONFIG_BOOKE)
-
+ if (val && !(val & DABR_TRANSLATION))
+ return false;
+#else
/* As described above, it was assumed 3 bits were passed with the data
* address, but we will assume only the mode bits will be passed
* as to not cause alignment restrictions for DAC-based processors.
*/

+ /* Read or Write bits must be set */
+ if (!(val & 0x3UL))
+ return -EINVAL;
+#endif
+ return true;
+}
+
+/**
+ * debugreg_update() - update a debug register associated with a task
+ * @task: The task whose register state is to be modified.
+ * @val: The value to be written to the debug register.
+ * @index: Specifies the debug register. Currently unused.
+ *
+ * Set a task's DABR/DAC to @val, which should be validated with
+ * debugreg_valid() beforehand.
+ */
+void debugreg_update(struct task_struct *task, unsigned long val,
+ unsigned int index)
+{
+#ifndef CONFIG_BOOKE
+ task->thread.dabr = val;
+#else
/* DAC's hold the whole address without any mode flags */
- task->thread.dabr = data & ~0x3UL;
+ task->thread.dabr = val & ~0x3UL;

if (task->thread.dabr == 0) {
task->thread.dbcr0 &= ~(DBSR_DAC1R | DBSR_DAC1W | DBCR0_IDM);
task->thread.regs->msr &= ~MSR_DE;
- return 0;
}

- /* Read or Write bits must be set */
-
- if (!(data & 0x3UL))
- return -EINVAL;
-
/* Set the Internal Debugging flag (IDM bit 1) for the DBCR0
register */
task->thread.dbcr0 = DBCR0_IDM;

/* Check for write and read flags and set DBCR0
accordingly */
- if (data & 0x1UL)
+ if (val & 0x1UL)
task->thread.dbcr0 |= DBSR_DAC1R;
- if (data & 0x2UL)
+ if (val & 0x2UL)
task->thread.dbcr0 |= DBSR_DAC1W;

task->thread.regs->msr |= MSR_DE;
#endif
+}
+
+static int ptrace_set_debugreg(struct task_struct *task, unsigned long addr,
+ unsigned long data)
+{
+ /* For ppc64 we support one DABR and no IABR's at the moment (ppc64).
+ * For embedded processors we support one DAC and no IAC's at the
+ * moment.
+ */
+ if (addr > 0)
+ return -EINVAL;
+
+ if (!debugreg_valid(data, 0))
+ return -EIO;
+
+ debugreg_update(task, data, 0);
+
return 0;
}

--
1.6.0.4

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