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Subject: Re: [PATCH v1 1/4] um: Fix ptrace GETREGS/SETREGS bugs
To: =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= <mic@digikod.net>,
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From: Richard Weinberger <richard@nod.at>
Message-ID: <5677BFBD.3090200@nod.at>
Date: Mon, 21 Dec 2015 10:00:45 +0100
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[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