[v2,2/2] arm64: Fix single stepping in kernel traps

Message ID 1507729721-53978-3-git-send-email-julien.thierry@arm.com
State New
Headers show
Series
  • Fix single step for traps
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Commit Message

Julien Thierry Oct. 11, 2017, 1:48 p.m.
Software Step exception is missing after stepping a trapped instruction.

Ensure SPSR.SS gets set to 0 after emulating/skipping a trapped instruction
before doing ERET.

Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>

---
 arch/arm64/include/asm/insn.h        |  5 +++++
 arch/arm64/include/asm/traps.h       |  6 ++++++
 arch/arm64/kernel/armv8_deprecated.c |  8 ++++----
 arch/arm64/kernel/cpufeature.c       |  2 +-
 arch/arm64/kernel/traps.c            | 21 ++++++++++++++++-----
 5 files changed, 32 insertions(+), 10 deletions(-)

--
1.9.1

Comments

Will Deacon Oct. 11, 2017, 2:37 p.m. | #1
On Wed, Oct 11, 2017 at 02:48:41PM +0100, Julien Thierry wrote:
> Software Step exception is missing after stepping a trapped instruction.
> 
> Ensure SPSR.SS gets set to 0 after emulating/skipping a trapped instruction
> before doing ERET.
> 
> Signed-off-by: Julien Thierry <julien.thierry@arm.com>
> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> 
> ---
>  arch/arm64/include/asm/insn.h        |  5 +++++
>  arch/arm64/include/asm/traps.h       |  6 ++++++
>  arch/arm64/kernel/armv8_deprecated.c |  8 ++++----
>  arch/arm64/kernel/cpufeature.c       |  2 +-
>  arch/arm64/kernel/traps.c            | 21 ++++++++++++++++-----
>  5 files changed, 32 insertions(+), 10 deletions(-)

[...]

> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index 5ea4b85..aaf9a523 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -293,6 +293,17 @@ void arm64_notify_die(const char *str, struct pt_regs *regs,
>  	}
>  }
> 
> +void arm64_setup_next_instr(struct pt_regs *regs, unsigned long size)
> +{
> +	regs->pc += size;
> +
> +	/*
> +	 * If we were single stepping, we want to get the step exception after
> +	 * we return from the trap.
> +	 */
> +	regs->pstate &= ~DBG_SPSR_SS;

Can you use user_fastforward_single_step instead, like we do for the signal
handling path?

Will
Julien Thierry Oct. 11, 2017, 3:06 p.m. | #2
On 11/10/17 15:37, Will Deacon wrote:
> On Wed, Oct 11, 2017 at 02:48:41PM +0100, Julien Thierry wrote:
>> Software Step exception is missing after stepping a trapped instruction.
>>
>> Ensure SPSR.SS gets set to 0 after emulating/skipping a trapped instruction
>> before doing ERET.
>>
>> Signed-off-by: Julien Thierry <julien.thierry@arm.com>
>> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will.deacon@arm.com>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>>
>> ---
>>   arch/arm64/include/asm/insn.h        |  5 +++++
>>   arch/arm64/include/asm/traps.h       |  6 ++++++
>>   arch/arm64/kernel/armv8_deprecated.c |  8 ++++----
>>   arch/arm64/kernel/cpufeature.c       |  2 +-
>>   arch/arm64/kernel/traps.c            | 21 ++++++++++++++++-----
>>   5 files changed, 32 insertions(+), 10 deletions(-)
> 
> [...]
> 
>> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
>> index 5ea4b85..aaf9a523 100644
>> --- a/arch/arm64/kernel/traps.c
>> +++ b/arch/arm64/kernel/traps.c
>> @@ -293,6 +293,17 @@ void arm64_notify_die(const char *str, struct pt_regs *regs,
>>   	}
>>   }
>>
>> +void arm64_setup_next_instr(struct pt_regs *regs, unsigned long size)
>> +{
>> +	regs->pc += size;
>> +
>> +	/*
>> +	 * If we were single stepping, we want to get the step exception after
>> +	 * we return from the trap.
>> +	 */
>> +	regs->pstate &= ~DBG_SPSR_SS;
> 
> Can you use user_fastforward_single_step instead, like we do for the signal
> handling path?

I guess we are always fast forwarding on the current task. So yes, I can 
use that.

Thanks,

Patch

diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
index 4214c38..de5e31a 100644
--- a/arch/arm64/include/asm/insn.h
+++ b/arch/arm64/include/asm/insn.h
@@ -22,6 +22,11 @@ 

 /* A64 instructions are always 32 bits. */
 #define	AARCH64_INSN_SIZE		4
+#define	AARCH32_INSN_SIZE		4
+
+/* Thumb/Thumb2 instruction sizes */
+#define	AARCH32_T32_INSN_SIZE		4
+#define	AARCH32_T16_INSN_SIZE		2

 #ifndef __ASSEMBLY__
 /*
diff --git a/arch/arm64/include/asm/traps.h b/arch/arm64/include/asm/traps.h
index d131501..67b971e 100644
--- a/arch/arm64/include/asm/traps.h
+++ b/arch/arm64/include/asm/traps.h
@@ -37,6 +37,12 @@  struct undef_hook {

 void arm64_notify_segfault(struct pt_regs *regs, unsigned long addr);

+/*
+ * Move regs->pc to next instruction and do necessary setup before it
+ * is executed.
+ */
+void arm64_setup_next_instr(struct pt_regs *regs, unsigned long size);
+
 static inline int __in_irqentry_text(unsigned long ptr)
 {
 	return ptr >= (unsigned long)&__irqentry_text_start &&
diff --git a/arch/arm64/kernel/armv8_deprecated.c b/arch/arm64/kernel/armv8_deprecated.c
index d06fbe4..2808e56 100644
--- a/arch/arm64/kernel/armv8_deprecated.c
+++ b/arch/arm64/kernel/armv8_deprecated.c
@@ -431,7 +431,7 @@  static int swp_handler(struct pt_regs *regs, u32 instr)
 	pr_warn_ratelimited("\"%s\" (%ld) uses obsolete SWP{B} instruction at 0x%llx\n",
 			current->comm, (unsigned long)current->pid, regs->pc);

-	regs->pc += 4;
+	arm64_setup_next_instr(regs, AARCH32_INSN_SIZE);
 	return 0;

 fault:
@@ -512,7 +512,7 @@  static int cp15barrier_handler(struct pt_regs *regs, u32 instr)
 	pr_warn_ratelimited("\"%s\" (%ld) uses deprecated CP15 Barrier instruction at 0x%llx\n",
 			current->comm, (unsigned long)current->pid, regs->pc);

-	regs->pc += 4;
+	arm64_setup_next_instr(regs, AARCH32_INSN_SIZE);
 	return 0;
 }

@@ -586,14 +586,14 @@  static int compat_setend_handler(struct pt_regs *regs, u32 big_endian)
 static int a32_setend_handler(struct pt_regs *regs, u32 instr)
 {
 	int rc = compat_setend_handler(regs, (instr >> 9) & 1);
-	regs->pc += 4;
+	arm64_setup_next_instr(regs, AARCH32_INSN_SIZE);
 	return rc;
 }

 static int t16_setend_handler(struct pt_regs *regs, u32 instr)
 {
 	int rc = compat_setend_handler(regs, (instr >> 3) & 1);
-	regs->pc += 2;
+	arm64_setup_next_instr(regs, AARCH32_T16_INSN_SIZE);
 	return rc;
 }

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 21e2c95..235834e 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1287,7 +1287,7 @@  static int emulate_mrs(struct pt_regs *regs, u32 insn)
 	if (!rc) {
 		dst = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RT, insn);
 		pt_regs_write_reg(regs, dst, val);
-		regs->pc += 4;
+		arm64_setup_next_instr(regs, AARCH64_INSN_SIZE);
 	}

 	return rc;
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 5ea4b85..aaf9a523 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -293,6 +293,17 @@  void arm64_notify_die(const char *str, struct pt_regs *regs,
 	}
 }

+void arm64_setup_next_instr(struct pt_regs *regs, unsigned long size)
+{
+	regs->pc += size;
+
+	/*
+	 * If we were single stepping, we want to get the step exception after
+	 * we return from the trap.
+	 */
+	regs->pstate &= ~DBG_SPSR_SS;
+}
+
 static LIST_HEAD(undef_hook);
 static DEFINE_RAW_SPINLOCK(undef_lock);

@@ -480,7 +491,7 @@  static void user_cache_maint_handler(unsigned int esr, struct pt_regs *regs)
 	if (ret)
 		arm64_notify_segfault(regs, address);
 	else
-		regs->pc += 4;
+		arm64_setup_next_instr(regs, AARCH64_INSN_SIZE);
 }

 static void ctr_read_handler(unsigned int esr, struct pt_regs *regs)
@@ -490,7 +501,7 @@  static void ctr_read_handler(unsigned int esr, struct pt_regs *regs)

 	pt_regs_write_reg(regs, rt, val);

-	regs->pc += 4;
+	arm64_setup_next_instr(regs, AARCH64_INSN_SIZE);
 }

 static void cntvct_read_handler(unsigned int esr, struct pt_regs *regs)
@@ -498,7 +509,7 @@  static void cntvct_read_handler(unsigned int esr, struct pt_regs *regs)
 	int rt = (esr & ESR_ELx_SYS64_ISS_RT_MASK) >> ESR_ELx_SYS64_ISS_RT_SHIFT;

 	pt_regs_write_reg(regs, rt, arch_counter_get_cntvct());
-	regs->pc += 4;
+	arm64_setup_next_instr(regs, AARCH64_INSN_SIZE);
 }

 static void cntfrq_read_handler(unsigned int esr, struct pt_regs *regs)
@@ -506,7 +517,7 @@  static void cntfrq_read_handler(unsigned int esr, struct pt_regs *regs)
 	int rt = (esr & ESR_ELx_SYS64_ISS_RT_MASK) >> ESR_ELx_SYS64_ISS_RT_SHIFT;

 	pt_regs_write_reg(regs, rt, arch_timer_get_rate());
-	regs->pc += 4;
+	arm64_setup_next_instr(regs, AARCH64_INSN_SIZE);
 }

 struct sys64_hook {
@@ -761,7 +772,7 @@  static int bug_handler(struct pt_regs *regs, unsigned int esr)
 	}

 	/* If thread survives, skip over the BUG instruction and continue: */
-	regs->pc += AARCH64_INSN_SIZE;	/* skip BRK and resume */
+	arm64_setup_next_instr(regs, AARCH64_INSN_SIZE);
 	return DBG_HOOK_HANDLED;
 }