This patch fixes an issue of having the stack be executable for x86 builds by ensuring that the two objects bios-rom.o and entry.o have the section .note.GNU-stack. Suggested-by: Alexandru Elisei <alexandru.elisei@xxxxxxx> Signed-off-by: Martin Radev <martin.b.radev@xxxxxxxxx> --- x86/bios/bios-rom.S | 5 +++++ x86/bios/entry.S | 5 +++++ 2 files changed, 10 insertions(+) diff --git a/x86/bios/bios-rom.S b/x86/bios/bios-rom.S index 3269ce9..d1c8b25 100644 --- a/x86/bios/bios-rom.S +++ b/x86/bios/bios-rom.S @@ -10,3 +10,8 @@ GLOBAL(bios_rom) .incbin "x86/bios/bios.bin" END(bios_rom) + +/* + * Add this section to ensure final binary has a non-executable stack. + */ +.section .note.GNU-stack,"",@progbits diff --git a/x86/bios/entry.S b/x86/bios/entry.S index 85056e9..1b71f89 100644 --- a/x86/bios/entry.S +++ b/x86/bios/entry.S @@ -90,3 +90,8 @@ GLOBAL(__locals) #include "local.S" END(__locals) + +/* + * Add this section to ensure final binary has a non-executable stack. + */ +.section .note.GNU-stack,"",@progbits -- 2.25.1 On Mon, Mar 14, 2022 at 05:11:08PM +0000, Alexandru Elisei wrote: > Hi, > > On Fri, Mar 11, 2022 at 11:23:21AM +0000, Andre Przywara wrote: > > On Thu, 10 Mar 2022 14:56:30 +0000 > > Alexandru Elisei <alexandru.elisei@xxxxxxx> wrote: > > > > Hi, > > > > > Hi Martin, > > > > > > On Fri, Mar 04, 2022 at 01:10:45AM +0200, Martin Radev wrote: > > > > Hello everyone, > > > > > > > [..] > > > > The Makefile change is kept in its original form because I didn't understand > > > > if there is an issue with it on aarch64. > > > > > > I'll try to explain it better. According to this blogpost about executable > > > stacks [1], gcc marks the stack as executable automatically for assembly > > > (.S) files. C files have their stack mark as non-executable by default. If > > > any of the object files have the stack executable, then the resulting > > > binary also has the stack marked as executable (obviously). > > > > > > To mark the stack as non-executable in assembly files, the empty section > > > .note.GNU-stack must be present in the file. This is a marking to tell > > > the linker that the final executable does not require an executable stack. > > > When the linker finds this section, it will create a PT_GNU_STACK empty > > > segment in the final executable. This segment tells Linux to mark the stack > > > as non-executable when it loads the binary. > > > > Ah, many thanks for the explanation, that makes sense. > > > > > The only assembly files that kvmtool compiles into objects are the x86 > > > files x86/bios/entry.S and x86/bios/bios-rom.S; the other architectures are > > > not affected by this. I haven't found any instances where these files (and > > > the other files they are including) do a call/jmp to something on the > > > stack, so I've added the .note.GNU-Stack section to the files: > > > > Yes, looks that the same to me, actually the assembly looks more like > > marshalling arguments than actual code, so we should be safe. > > > > Alex, can you send this as a proper patch. It should be somewhat > > independent of Martin's series, code-wise, so at least it should apply and > > build. > > Martin, would you like to pick up the diff and turn it into a proper patch? You > don't need to credit me as the author, you can just add a Suggested-by: > Alexandru Elisei <alexandru.elisei@xxxxxxx> tag in the commit message. Or do you > want me to turn this into a patch? If I do, I'll add a Reported-by: Martin Radev > <martin.b.radev@xxxxxxxxx> tag to it. > > I don't have a preference, I am asking because you were the first person who > discovered and tried to fix this. > > Thanks, > Alex > > > > > Cheers, > > Andre > > > > > > > > diff --git a/x86/bios/bios-rom.S b/x86/bios/bios-rom.S > > > index 3269ce9793ae..571029fc157e 100644 > > > --- a/x86/bios/bios-rom.S > > > +++ b/x86/bios/bios-rom.S > > > @@ -10,3 +10,6 @@ > > > GLOBAL(bios_rom) > > > .incbin "x86/bios/bios.bin" > > > END(bios_rom) > > > + > > > +# Mark the stack as non-executable. > > > +.section .note.GNU-stack,"",@progbits > > > diff --git a/x86/bios/entry.S b/x86/bios/entry.S > > > index 85056e9816c4..4d5bb663a25d 100644 > > > --- a/x86/bios/entry.S > > > +++ b/x86/bios/entry.S > > > @@ -90,3 +90,6 @@ GLOBAL(__locals) > > > #include "local.S" > > > > > > END(__locals) > > > + > > > +# Mark the stack as non-executable. > > > +.section .note.GNU-stack,"",@progbits > > > > > > which makes the final executable have a non-executable stack. Did some very > > > *light* testing by booting a guest, and everything looked right to me. > > > > > > [1] https://www.airs.com/blog/archives/518 > > > > > > Thanks, > > > Alex > > > > > > > > > > > Martin Radev (5): > > > > kvmtool: Add WARN_ONCE macro > > > > virtio: Sanitize config accesses > > > > virtio: Check for overflows in QUEUE_NOTIFY and QUEUE_SEL > > > > Makefile: Mark stack as not executable > > > > mmio: Sanitize addr and len > > > > > > > > Makefile | 7 +++-- > > > > include/kvm/util.h | 10 +++++++ > > > > include/kvm/virtio-9p.h | 1 + > > > > include/kvm/virtio.h | 3 ++- > > > > mmio.c | 4 +++ > > > > virtio/9p.c | 27 ++++++++++++++----- > > > > virtio/balloon.c | 10 ++++++- > > > > virtio/blk.c | 10 ++++++- > > > > virtio/console.c | 10 ++++++- > > > > virtio/mmio.c | 44 +++++++++++++++++++++++++----- > > > > virtio/net.c | 12 +++++++-- > > > > virtio/pci.c | 59 ++++++++++++++++++++++++++++++++++++++--- > > > > virtio/rng.c | 8 +++++- > > > > virtio/scsi.c | 10 ++++++- > > > > virtio/vsock.c | 10 ++++++- > > > > 15 files changed, 199 insertions(+), 26 deletions(-) > > > > > > > > -- > > > > 2.25.1 > > > > > >
