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Date: Fri, 22 Jan 2016 13:23:23 -0800
From: Kees Cook <>
To: Alexei Starovoitov <>
Cc: Daniel Sangorrin <>, Andy Lutomirski <>, 
	Will Drewry <>, LKML <>, 
	Linux API <>, 
	"" <>
Subject: Re: [RFC PATCH 1/1] seccomp: provide information about the previous syscall

On Fri, Jan 22, 2016 at 9:30 AM, Alexei Starovoitov
<> wrote:
> On Fri, Jan 22, 2016 at 03:30:00PM +0900, Daniel Sangorrin wrote:
>> This patch allows applications to restrict the order in which
>> its system calls may be requested. In order to do that, we
>> provide seccomp-BPF scripts with information about the
>> previous system call requested.
>> An example use case consists of detecting (and stopping) return
>> oriented attacks that disturb the normal execution flow of
>> a user program.
>> Signed-off-by: Daniel Sangorrin <>
> ...
>> diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h
> ...
>>  struct seccomp_data {
>>       int nr;
>> +     int prev_nr;
>>       __u32 arch;
>>       __u64 instruction_pointer;
>>       __u64 args[6];
> this will break abi for existing seccomp programs.
> New field has to be at the end.

Yeah, and if we break abi, we need to add further sanity checking to
the parser to determine which "version" of seccomp_data we need. I'm
not convinced that there is enough utility here to break ABI.

(Though if we do, I'd like to add tid to the seccomp_data, which has
been requested in the past to make some pid-based arg checks easier to


Kees Cook
Chrome OS & Brillo Security

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