On Tue, Mar 13, 2018 at 04:16:27PM -0700, Howard McLauchlan wrote:
> Error injection is a useful mechanism to fail arbitrary kernel
> functions. However, it is often hard to guarantee an error propagates
> appropriately to user space programs. By injecting into syscalls, we can
> return arbitrary values to user space directly; this increases
> flexibility and robustness in testing, allowing us to test user space
> error paths effectively.
>
> The following script, for example, fails calls to sys_open() from a
> given pid:
>
> from bcc import BPF
> from sys import argv
>
> pid = argv[1]
>
> prog = r"""
>
> int kprobe__SyS_open(struct pt_regs *ctx, const char *pathname, int flags)
> {
> u32 pid = bpf_get_current_pid_tgid();
> if (pid == %s)
> bpf_override_return(ctx, -ENOENT);
> return 0;
> }
> """ % pid
>
> b = BPF(text = prog)
> while 1:
> b.perf_buffer_poll()
>
> This patch whitelists all syscalls defined with SYSCALL_DEFINE for error
> injection.
>
> Signed-off-by: Howard McLauchlan <hmclauch...@fb.com>
> ---
> based on 4.16-rc5
> include/linux/syscalls.h | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index a78186d826d7..e8c6d63ace78 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -191,6 +191,8 @@ static inline int is_syscall_trace_event(struct
> trace_event_call *tp_event)
>
> #define SYSCALL_DEFINE0(sname) \
> SYSCALL_METADATA(_##sname, 0); \
> + asmlinkage long sys_##sname(void); \
> + ALLOW_ERROR_INJECTION(sys_##sname, ERRNO); \
> asmlinkage long sys_##sname(void)
>
> #define SYSCALL_DEFINE1(name, ...) SYSCALL_DEFINEx(1, _##name, __VA_ARGS__)
> @@ -210,6 +212,7 @@ static inline int is_syscall_trace_event(struct
> trace_event_call *tp_event)
> #define __SYSCALL_DEFINEx(x, name, ...)
> \
> asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
> __attribute__((alias(__stringify(SyS##name)))); \
> + ALLOW_ERROR_INJECTION(sys##name, ERRNO); \
> static inline long SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__)); \
> asmlinkage long SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__)); \
> asmlinkage long SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
> --
> 2.14.1
>
Adding a few more people to Cc
