llvm dev - Feb 2016 - [RFC] Embedding Bitcode in Object Files

I don't know whether this is an issue in the current implementation, but I
wanted to bring up a potential privacy issue.

In embedding the information, care should be taken to avoid embedding any
information that contains personally identifiable information. This can
certainly occur
if paths need to be embedded, as user names, or other private/confidential
information may be present in the naming of directories and paths.  Generally, I
suspect
that it would be desirable to have an opt-in strategy for designating in the
compiler which pieces of information/options need to be saved, and for all
options marked
as needed, determine whether there is the possibility/likelihood that they may
contain personally identifiable information.

Kevin B. Smith

From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of James Y
Knight via llvm-dev
Sent: Friday, February 05, 2016 3:13 PM
To: Steven Wu <stevenwu at apple.com>
Cc: LLVM Developers Mailing List <llvm-dev at lists.llvm.org>; Clang Dev
<cfe-dev at lists.llvm.org>
Subject: Re: [llvm-dev] [RFC] Embedding Bitcode in Object Files



On Fri, Feb 5, 2016 at 6:06 PM, Steven Wu <stevenwu at
apple.com<mailto:stevenwu at apple.com>> wrote:
I don't think we need any path in the command line section. We only record
the command-line options that will affect CodeGen. See my example in one of the
preview reply:
$ clang -fembed-bitcode -O0 test.c -c -###
"clang" "-cc1"  (...lots of options...) "-o"
"test.bc" "-x" "c" "test.c"   <---
First stage
"clang" "-cc1" "-triple"
"x86_64-apple-macosx10.11.0" "-emit-obj"
"-fembed-bitcode" "-O0" "-disable-llvm-optzns"
"-o" "test.o" "-x" "ir"
"test.bc"  <--- Second stage
I can't think of any source path that can affect CodeGen. There should not
be any paths other than the bitcode input path and binary output path exists in
the second stage and they are excluded from the command line section as well.
-fdebug-prefix-map is consumed by the front-end and prefixed paths are a part of
the debug info in the metadata. You don't need to encode -fdebug-prefix-map
in the bitcode section to reproduce the object file with the same debug info.
Did that answer your concern?

Great -- it wasn't clear from the first message if you were just embedding
the whole command-line as is. If the plan instead to embed only a few relevant
options, I agree there should be no issue as far as paths go.
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----- Original Message -----
> From: "Kevin B via llvm-dev Smith" <llvm-dev at
lists.llvm.org>
> To: "James Y Knight" <jyknight at google.com>, "Steven
Wu"
> <stevenwu at apple.com>
> Cc: llvm-dev at lists.llvm.org, "Clang Dev" <cfe-dev at
lists.llvm.org>
> Sent: Saturday, February 6, 2016 4:30:20 PM
> Subject: Re: [llvm-dev] [RFC] Embedding Bitcode in Object Files
> I don't know whether this is an issue in the current implementation,
> but I wanted to bring up a potential privacy issue.
> In embedding the information, care should be taken to avoid embedding
> any information that contains personally identifiable information.
> This can certainly occur
> if paths need to be embedded, as user names, or other
> private/confidential information may be present in the naming of
> directories and paths.
Is this any more of a problem than the information that gets included in the
DWARF sections?

-Hal 
> Generally, I suspect
> that it would be desirable to have an opt-in strategy for designating
> in the compiler which pieces of information/options need to be
> saved, and for all options marked
> as needed, determine whether there is the possibility/likelihood that
> they may contain personally identifiable information.
> Kevin B. Smith
> From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of
> James Y Knight via llvm-dev
> Sent: Friday, February 05, 2016 3:13 PM
> To: Steven Wu <stevenwu at apple.com>
> Cc: LLVM Developers Mailing List <llvm-dev at lists.llvm.org>; Clang
Dev
> <cfe-dev at lists.llvm.org>
> Subject: Re: [llvm-dev] [RFC] Embedding Bitcode in Object Files
> On Fri, Feb 5, 2016 at 6:06 PM, Steven Wu < stevenwu at apple.com >
> wrote:
> > I don't think we need any path in the command line section. We
only
> > record the command-line options that will affect CodeGen. See my
> > example in one of the preview reply:
> 
> > > $ clang -fembed-bitcode -O0 test.c -c -###
> > 
> 
> > > "clang" "-cc1" (...lots of options...)
"-o" "test.bc" "-x" "c"
> > > "test.c" <--- First stage
> > 
> 
> > > "clang" "-cc1" "-triple"
"x86_64-apple-macosx10.11.0" "-emit-obj"
> > > "-fembed-bitcode" "-O0"
"-disable-llvm-optzns" "-o" "test.o"
"-x"
> > > "ir" "test.bc" <--- Second stage
> > 
> 
> > I can't think of any source path that can affect CodeGen. There
> > should not be any paths other than the bitcode input path and
> > binary
> > output path exists in the second stage and they are excluded from
> > the command line section as well. -fdebug-prefix-map is consumed by
> > the front-end and prefixed paths are a part of the debug info in
> > the
> > metadata. You don't need to encode -fdebug-prefix-map in the
> > bitcode
> > section to reproduce the object file with the same debug info. Did
> > that answer your concern?
> 
> Great -- it wasn't clear from the first message if you were just
> embedding the whole command-line as is. If the plan instead to embed
> only a few relevant options, I agree there should be no issue as far
> as paths go.
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
-- 

Hal Finkel 
Assistant Computational Scientist 
Leadership Computing Facility 
Argonne National Laboratory 
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Hal,

No, it is not more of a problem than with DWARF info. DWARF info definitely
contains personally identifiable information.  However, people usually realize
that is the case,
and will turn off or strip debug info if they are worried about such issues, or
make a specific plan to cleanse that information.

You really just want to attempt to eliminate such information to the greatest
extent possible.  The desirability of using embedded Bitcode in libraries (which
is a very
natural use model, that I'm pretty sure this is intended to support), will
be improved by taking into consideration this aspect of the implementation.

Kevin Smith



From: Hal Finkel [mailto:hfinkel at anl.gov]
Sent: Saturday, February 06, 2016 2:37 PM
To: Smith, Kevin B <kevin.b.smith at intel.com>
Cc: llvm-dev at lists.llvm.org; Clang Dev <cfe-dev at lists.llvm.org>;
James Y Knight <jyknight at google.com>; Steven Wu <stevenwu at
apple.com>
Subject: Re: [llvm-dev] [RFC] Embedding Bitcode in Object Files


________________________________
From: "Kevin B via llvm-dev Smith" <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>>
To: "James Y Knight" <jyknight at google.com<mailto:jyknight at
google.com>>, "Steven Wu" <stevenwu at
apple.com<mailto:stevenwu at apple.com>>
Cc: llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>,
"Clang Dev" <cfe-dev at lists.llvm.org<mailto:cfe-dev at
lists.llvm.org>>
Sent: Saturday, February 6, 2016 4:30:20 PM
Subject: Re: [llvm-dev] [RFC] Embedding Bitcode in Object Files
I don't know whether this is an issue in the current implementation, but I
wanted to bring up a potential privacy issue.

In embedding the information, care should be taken to avoid embedding any
information that contains personally identifiable information. This can
certainly occur
if paths need to be embedded, as user names, or other private/confidential
information may be present in the naming of directories and paths.

Is this any more of a problem than the information that gets included in the
DWARF sections?

 -Hal
  Generally, I suspect
that it would be desirable to have an opt-in strategy for designating in the
compiler which pieces of information/options need to be saved, and for all
options marked
as needed, determine whether there is the possibility/likelihood that they may
contain personally identifiable information.

Kevin B. Smith

From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of James Y
Knight via llvm-dev
Sent: Friday, February 05, 2016 3:13 PM
To: Steven Wu <stevenwu at apple.com<mailto:stevenwu at apple.com>>
Cc: LLVM Developers Mailing List <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>>; Clang Dev
<cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>>
Subject: Re: [llvm-dev] [RFC] Embedding Bitcode in Object Files



On Fri, Feb 5, 2016 at 6:06 PM, Steven Wu <stevenwu at
apple.com<mailto:stevenwu at apple.com>> wrote:
I don't think we need any path in the command line section. We only record
the command-line options that will affect CodeGen. See my example in one of the
preview reply:
$ clang -fembed-bitcode -O0 test.c -c -###
"clang" "-cc1"  (...lots of options...) "-o"
"test.bc" "-x" "c" "test.c"   <---
First stage
"clang" "-cc1" "-triple"
"x86_64-apple-macosx10.11.0" "-emit-obj"
"-fembed-bitcode" "-O0" "-disable-llvm-optzns"
"-o" "test.o" "-x" "ir"
"test.bc"  <--- Second stage
I can't think of any source path that can affect CodeGen. There should not
be any paths other than the bitcode input path and binary output path exists in
the second stage and they are excluded from the command line section as well.
-fdebug-prefix-map is consumed by the front-end and prefixed paths are a part of
the debug info in the metadata. You don't need to encode -fdebug-prefix-map
in the bitcode section to reproduce the object file with the same debug info.
Did that answer your concern?

Great -- it wasn't clear from the first message if you were just embedding
the whole command-line as is. If the plan instead to embed only a few relevant
options, I agree there should be no issue as far as paths go.

_______________________________________________
LLVM Developers mailing list
llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev



--
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory
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