[musl] Mark stack as non-executable in asm

[musl] Mark stack as non-executable in asm

[Norbert Lange]

Hello,

I did borrow some assembler files to avoid having to link against
(any) libc. That was for building a DSO, ultimately loaded via glibc.
The effect was that glibc did change the protection of all stacks to
be executable.

Would you consider adding the line [1]
.section        .note.GNU-stack, "", %progbits
to assembly files?

I know this is not a musl bug, and I can easily add the lines myself.

regards, Norbert

[1] - https://wiki.ubuntu.com/SecurityTeam/Roadmap/ExecutableStacks

Re: [musl] Mark stack as non-executable in asm

[Szabolcs Nagy]

* Norbert Lange <nolange79@gmail.com> [2020-06-10 11:24:04 +0200]:
> I did borrow some assembler files to avoid having to link against
> (any) libc. That was for building a DSO, ultimately loaded via glibc.
> The effect was that glibc did change the protection of all stacks to
> be executable.
> 
> Would you consider adding the line [1]
> .section        .note.GNU-stack, "", %progbits
> to assembly files?
> 
> I know this is not a musl bug, and I can easily add the lines myself.

musl build system (just like other libcs i know of)
pass -noexecstack to the assembler so if you build
the asm files as part of libc the object files should
have the marking, if you build outside of libc i
think it's your responsibility to add the note
(either to the asm or via the -Wa,-noexecstack flag)

readelf -lW libfoo.so | grep GNU_STACK

is one way to verify that everything has the note.

> 
> regards, Norbert
> 
> [1] - https://wiki.ubuntu.com/SecurityTeam/Roadmap/ExecutableStacks

Re: [musl] Mark stack as non-executable in asm

[Jeffrey Walton]

On Wed, Jun 10, 2020 at 6:31 AM Szabolcs Nagy <nsz@port70.net> wrote:
>
> * Norbert Lange <nolange79@gmail.com> [2020-06-10 11:24:04 +0200]:
> > I did borrow some assembler files to avoid having to link against
> > (any) libc. That was for building a DSO, ultimately loaded via glibc.
> > The effect was that glibc did change the protection of all stacks to
> > be executable.
> >
> > Would you consider adding the line [1]
> > .section        .note.GNU-stack, "", %progbits
> > to assembly files?
> >
> > I know this is not a musl bug, and I can easily add the lines myself.
>
> musl build system (just like other libcs i know of)
> pass -noexecstack to the assembler so if you build
> the asm files as part of libc the object files should
> have the marking, if you build outside of libc i
> think it's your responsibility to add the note
> (either to the asm or via the -Wa,-noexecstack flag)
>
> readelf -lW libfoo.so | grep GNU_STACK
>
> is one way to verify that everything has the note.

It may be worth mentioning, according to the Binutil folks, the stack
size has to be 0. A non-0 stack size means executable stacks are in
effect. In the case of non-0, I believe the loader is responsible for
loss of the nx-stack.

Jeff

Re: [musl] Mark stack as non-executable in asm

[Norbert Lange]

Am Mi., 10. Juni 2020 um 12:31 Uhr schrieb Szabolcs Nagy <nsz@port70.net>:
>
> * Norbert Lange <nolange79@gmail.com> [2020-06-10 11:24:04 +0200]:
> > I did borrow some assembler files to avoid having to link against
> > (any) libc. That was for building a DSO, ultimately loaded via glibc.
> > The effect was that glibc did change the protection of all stacks to
> > be executable.
> >
> > Would you consider adding the line [1]
> > .section        .note.GNU-stack, "", %progbits
> > to assembly files?
> >
> > I know this is not a musl bug, and I can easily add the lines myself.
>
> musl build system (just like other libcs i know of)
> pass -noexecstack to the assembler so if you build
> the asm files as part of libc the object files should
> have the marking, if you build outside of libc i
> think it's your responsibility to add the note
> (either to the asm or via the -Wa,-noexecstack flag)
>
> readelf -lW libfoo.so | grep GNU_STACK
>
> is one way to verify that everything has the note.

Yeah easy to do, just may take a lot time till you figure out why just
sometimes your app gets its stack remapped.
I understand your position, the aim was to safe other people such trouble.

Norbert