[PATCH v2] arm64: kgdb: handle read-only text / modules

[Mark Rutland]

On Wed, Sep 21, 2016 at 04:19:55PM +0900, AKASHI Takahiro wrote:
> Handle read-only cases (CONFIG_DEBUG_RODATA/CONFIG_DEBUG_SET_MODULE_RONX)
> by using aarch64_insn_write() instead of probe_kernel_write().
> See how this works:
>     commit 2f896d586610 ("arm64: use fixmap for text patching")
> 
> Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Will Deacon <will.deacon at arm.com>
> Cc: Jason Wessel <jason.wessel at windriver.com>
> Cc: <stable at vger.kernel.org> # 3.18-3.19: 2f896d5: arm64: use fixmap
> Cc: <stable at vger.kernel.org> # 4.0-

For v3.18-v3.19, we also need commit f6242cac10427c54 ("arm64: Fix text
patching logic when using fixmap"), so as to not break the
!CONFIG_DEBUG_SET_MODULE_RONX case.

With that:

Reviewed-by: Mark Rutland <mark.rutland at arm.com>

Thanks,
Mark.

> ---
>  arch/arm64/include/asm/debug-monitors.h |  2 --
>  arch/arm64/kernel/kgdb.c                | 36 ++++++++++++++++++++++-----------
>  2 files changed, 24 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/debug-monitors.h b/arch/arm64/include/asm/debug-monitors.h
> index 4b6b3f7..b71420a 100644
> --- a/arch/arm64/include/asm/debug-monitors.h
> +++ b/arch/arm64/include/asm/debug-monitors.h
> @@ -61,8 +61,6 @@
>  
>  #define AARCH64_BREAK_KGDB_DYN_DBG	\
>  	(AARCH64_BREAK_MON | (KGDB_DYN_DBG_BRK_IMM << 5))
> -#define KGDB_DYN_BRK_INS_BYTE(x)	\
> -	((AARCH64_BREAK_KGDB_DYN_DBG >> (8 * (x))) & 0xff)
>  
>  #define CACHE_FLUSH_IS_SAFE		1
>  
> diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c
> index 6732a27..b06a7a2 100644
> --- a/arch/arm64/kernel/kgdb.c
> +++ b/arch/arm64/kernel/kgdb.c
> @@ -19,6 +19,7 @@
>   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
>   */
>  
> +#include <linux/bug.h>
>  #include <linux/cpumask.h>
>  #include <linux/irq.h>
>  #include <linux/irq_work.h>
> @@ -26,6 +27,8 @@
>  #include <linux/kgdb.h>
>  #include <linux/kprobes.h>
>  #include <linux/percpu.h>
> +#include <asm/debug-monitors.h>
> +#include <asm/insn.h>
>  #include <asm/ptrace.h>
>  #include <asm/traps.h>
>  
> @@ -370,15 +373,24 @@ void kgdb_arch_exit(void)
>  	unregister_die_notifier(&kgdb_notifier);
>  }
>  
> -/*
> - * ARM instructions are always in LE.
> - * Break instruction is encoded in LE format
> - */
> -struct kgdb_arch arch_kgdb_ops = {
> -	.gdb_bpt_instr = {
> -		KGDB_DYN_BRK_INS_BYTE(0),
> -		KGDB_DYN_BRK_INS_BYTE(1),
> -		KGDB_DYN_BRK_INS_BYTE(2),
> -		KGDB_DYN_BRK_INS_BYTE(3),
> -	}
> -};
> +struct kgdb_arch arch_kgdb_ops;
> +
> +int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
> +{
> +	int err;
> +
> +	BUILD_BUG_ON(AARCH64_INSN_SIZE != BREAK_INSTR_SIZE);
> +
> +	err = aarch64_insn_read((void *)bpt->bpt_addr, (u32 *)bpt->saved_instr);
> +	if (err)
> +		return err;
> +
> +	return aarch64_insn_write((void *)bpt->bpt_addr,
> +			(u32)AARCH64_BREAK_KGDB_DYN_DBG);
> +}
> +
> +int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
> +{
> +	return aarch64_insn_write((void *)bpt->bpt_addr,
> +			*(u32 *)bpt->saved_instr);
> +}
> -- 
> 2.10.0
>