PTRACE_GET_SYSCALL_INFO is a generic ptrace API that lets ptracer obtain
details of the syscall the tracee is blocked in.
There are two reasons for a special syscall-related ptrace request.
Firstly, with the current ptrace API there are cases when ptracer cannot
retrieve necessary information about syscalls. Some examples include:
* The notorious int-0x80-from-64-bit-task issue. See [1] for details.
In short, if a 64-bit task performs a syscall through int 0x80, its
tracer has no reliable means to find out that the syscall was, in
fact, a compat syscall, and misidentifies it.
* Syscall-enter-stop and syscall-exit-stop look the same for the
tracer. Common practice is to keep track of the sequence of
ptrace-stops in order not to mix the two syscall-stops up. But it is
not as simple as it looks; for example, strace had a (just recently
fixed) long-standing bug where attaching strace to a tracee that is
performing the execve system call led to the tracer identifying the
following syscall-exit-stop as syscall-enter-stop, which messed up
all the state tracking.
* Since the introduction of commit 84d77d3f06 ("ptrace: Don't allow
accessing an undumpable mm"), both PTRACE_PEEKDATA and
process_vm_readv become unavailable when the process dumpable flag is
cleared. On such architectures as ia64 this results in all syscall
arguments being unavailable for the tracer.
Secondly, ptracers also have to support a lot of arch-specific code for
obtaining information about the tracee. For some architectures, this
requires a ptrace(PTRACE_PEEKUSER, ...) invocation for every syscall
argument and return value.
PTRACE_GET_SYSCALL_INFO returns the following structure:
struct ptrace_syscall_info {
__u8 op; /* PTRACE_SYSCALL_INFO_* */
__u32 arch __attribute__((__aligned__(sizeof(__u32))));
__u64 instruction_pointer;
__u64 stack_pointer;
union {
struct {
__u64 nr;
__u64 args[6];
} entry;
struct {
__s64 rval;
__u8 is_error;
} exit;
struct {
__u64 nr;
__u64 args[6];
__u32 ret_data;
} seccomp;
};
};
The structure was chosen according to [2], except for the following
changes:
* seccomp substructure was added as a superset of entry substructure
* the type of nr field was changed from int to __u64 because syscall
numbers are, as a practical matter, 64 bits
* stack_pointer field was added along with instruction_pointer field
since it is readily available and can save the tracer from extra
PTRACE_GETREGS/PTRACE_GETREGSET calls
* arch is always initialized to aid with tracing system calls such as
execve()
* instruction_pointer and stack_pointer are always initialized so they
could be easily obtained for non-syscall stops
* a boolean is_error field was added along with rval field, this way
the tracer can more reliably distinguish a return value from an error
value
strace has been ported to PTRACE_GET_SYSCALL_INFO. Starting with
release 4.26, strace uses PTRACE_GET_SYSCALL_INFO API as the preferred
mechanism of obtaining syscall information.
[1] https://lore.kernel.org/lkml/CA+55aFzcSVmdDj9Lh_gdbz1OzHyEm6ZrGPBDAJnywm2LF_eVyg@mail.gmail.com/
[2] https://lore.kernel.org/lkml/CAObL_7GM0n80N7J_DFw_eQyfLyzq+sf4y2AvsCCV88Tb3AwEHA@mail.gmail.com/
This patch (of 7):
All syscall_get_*() and syscall_set_*() functions must be defined as
static inline as on all other architectures, otherwise asm/syscall.h
cannot be included in more than one compilation unit.
This bug has to be fixed in order to extend the generic
ptrace API with PTRACE_GET_SYSCALL_INFO request.
Link: http://lkml.kernel.org/r/20190510152749.GA28558@altlinux.org
Fixes: 1932fbe36e ("nds32: System calls handling")
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Reported-by: kbuild test robot <lkp@intel.com>
Acked-by: Greentime Hu <greentime@andestech.com>
Cc: Vincent Chen <deanbo422@gmail.com>
Cc: Elvira Khabirova <lineprinter@altlinux.org>
Cc: Eugene Syromyatnikov <esyr@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Helge Deller <deller@gmx.de> [parisc]
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
33644b95eb