On Thu, 2018-06-07 at 15:22 +0530, Naveen N. Rao wrote:
> We implement regs_set_return_value() and override_function_with_return()
> for this purpose.
>
> On powerpc, a return from a function (blr) just branches to the location
> contained in the link register. So, we can just update pt_regs rather
> than redirecting execution to a dummy function that returns.
>
> Signed-off-by: Naveen N. Rao
> ---
> The only change is to add a comment in override_function_with_return()
> to clarify that we don't need to worry about 32-bit userspace while
> emulating 'blr'.
Reviewed-by: Samuel Mendoza-Jonas
>
> - Naveen
>
> arch/powerpc/Kconfig | 1 +
> arch/powerpc/include/asm/error-injection.h | 13 +
> arch/powerpc/include/asm/ptrace.h | 5 +
> arch/powerpc/lib/Makefile | 2 ++
> arch/powerpc/lib/error-inject.c| 16
> 5 files changed, 37 insertions(+)
> create mode 100644 arch/powerpc/include/asm/error-injection.h
> create mode 100644 arch/powerpc/lib/error-inject.c
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 076fe3094856..00dad3c759a0 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -187,6 +187,7 @@ config PPC
> select HAVE_EBPF_JITif PPC64
> select HAVE_EFFICIENT_UNALIGNED_ACCESS if !(CPU_LITTLE_ENDIAN &&
> POWER7_CPU)
> select HAVE_FTRACE_MCOUNT_RECORD
> + select HAVE_FUNCTION_ERROR_INJECTION
> select HAVE_FUNCTION_GRAPH_TRACER
> select HAVE_FUNCTION_TRACER
> select HAVE_GCC_PLUGINS
> diff --git a/arch/powerpc/include/asm/error-injection.h
> b/arch/powerpc/include/asm/error-injection.h
> new file mode 100644
> index ..740c3075bdf4
> --- /dev/null
> +++ b/arch/powerpc/include/asm/error-injection.h
> @@ -0,0 +1,13 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +#ifndef _ASM_ERROR_INJECTION_H
> +#define _ASM_ERROR_INJECTION_H
> +
> +#include
> +#include
> +#include
> +#include
> +
> +void override_function_with_return(struct pt_regs *regs);
> +
> +#endif /* _ASM_ERROR_INJECTION_H */
> diff --git a/arch/powerpc/include/asm/ptrace.h
> b/arch/powerpc/include/asm/ptrace.h
> index e4923686e43a..c0705296c2f0 100644
> --- a/arch/powerpc/include/asm/ptrace.h
> +++ b/arch/powerpc/include/asm/ptrace.h
> @@ -101,6 +101,11 @@ static inline long regs_return_value(struct pt_regs
> *regs)
> return -regs->gpr[3];
> }
>
> +static inline void regs_set_return_value(struct pt_regs *regs, unsigned long
> rc)
> +{
> + regs->gpr[3] = rc;
> +}
> +
> #ifdef __powerpc64__
> #define user_mode(regs) regs)->msr) >> MSR_PR_LG) & 0x1)
> #else
> diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
> index d0ca13ad8231..dd43c5a53396 100644
> --- a/arch/powerpc/lib/Makefile
> +++ b/arch/powerpc/lib/Makefile
> @@ -14,6 +14,8 @@ obj-y += string.o alloc.o code-patching.o feature-fixups.o
>
> obj-$(CONFIG_PPC32) += div64.o copy_32.o crtsavres.o
>
> +obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
> +
> # See corresponding test in arch/powerpc/Makefile
> # 64-bit linker creates .sfpr on demand for final link (vmlinux),
> # so it is only needed for modules, and only for older linkers which
> diff --git a/arch/powerpc/lib/error-inject.c b/arch/powerpc/lib/error-inject.c
> new file mode 100644
> index ..407b992fb02f
> --- /dev/null
> +++ b/arch/powerpc/lib/error-inject.c
> @@ -0,0 +1,16 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +#include
> +#include
> +#include
> +
> +void override_function_with_return(struct pt_regs *regs)
> +{
> + /*
> + * Emulate 'blr'. 'regs' represents the state on entry of a predefined
> + * function in the kernel/module, captured on a kprobe. We don't need
> + * to worry about 32-bit userspace on a 64-bit kernel.
> + */
> + regs->nip = regs->link;
> +}
> +NOKPROBE_SYMBOL(override_function_with_return);
