Re: [PATCH v1 1/4] um: Fix ptrace GETREGS/SETREGS bugs

Richard Weinberger
2015-12-21T09:00:50Z

[sending the mail again, Thunderbird crashed :-\]

Am 21.12.2015 um 09:49 schrieb Mickaël Salaün:
>
> On 21/12/2015 01:20, Richard Weinberger wrote:
>> Am 21.12.2015 um 01:03 schrieb Mickaël Salaün:
>>> diff --git a/arch/um/kernel/skas/syscall.c b/arch/um/kernel/skas/syscall.c
>>> index 1683b8e..65f0d1a 100644
>>> --- a/arch/um/kernel/skas/syscall.c
>>> +++ b/arch/um/kernel/skas/syscall.c
>>> @@ -7,6 +7,7 @@
>>> #include <linux/ptrace.h>
>>> #include <kern_util.h>
>>> #include <sysdep/ptrace.h>
>>> +#include <sysdep/ptrace_user.h>
>>> #include <sysdep/syscalls.h>
>>> #include <os.h>
>>>
>>> @@ -16,12 +17,16 @@ void handle_syscall(struct uml_pt_regs *r)
>>> long result;
>>> int syscall;
>>>
>>> + /* Save the syscall register. */
>>> + UPT_SYSCALL_NR(r) = PT_SYSCALL_NR(r->gp);
>>> +
>>> if (syscall_trace_enter(regs)) {
>>> result = -ENOSYS;
>>> goto out;
>>> }
>>>
>>> - syscall = get_syscall(r);
>>> + /* Get the syscall after being potentially updated with ptrace. */
>>> + syscall = UPT_SYSCALL_NR(r);
>>
>> Doesn't this break the support for changing syscall numbers using PTRACE_SETREGS?
>
> The logic is unchanged except updating the UPT_SYSCALL_NR before syscall_trace_enter(). I did my last tests with the x86_32 subarchitecture and all tests (from selftest/seccomp), including PTRACE_SETREGS for syscall numbers tests, passed. However, 2 of this tests still fail for x86_64 (only).

No, the logic is different.
syscall_trace_enter(regs) enters the ptrace() path and here registers can be changed.
Hence "syscall = UPT_SYSCALL_NR(r);" will see the old syscall number.
UPT_SYSCALL_NR() returns the syscall number before the ptrace() path...

Thanks,
//richard