Messages in this thread | | | From | "H.J. Lu" <> | Date | Wed, 9 Aug 2017 11:46:24 -0700 | Subject | Re: new ELF marking |
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On Wed, Aug 9, 2017 at 11:26 AM, Kees Cook <keescook@google.com> wrote: > On Wed, Aug 9, 2017 at 10:16 AM, H.J. Lu <hjl.tools@gmail.com> wrote: >> On Wed, Aug 9, 2017 at 10:07 AM, Kees Cook via binutils >> <binutils@sourceware.org> wrote: >>> Hi, >>> >>> I'd like to be able to mark an ELF binary in such a way that Linux's >>> binfmt_elf.c will collapse a PIE text area into the mmap region >>> (currently they are separately randomized in memory). This is desired >>> by AddressSanitizer to avoid having an ASan-built binary have its text >>> area moving into an unexpected location[1] (ASLR is still desired, but >>> doesn't need to have a PIE/mmap split). >>> >>> I see a few ways: >>> >>> - Add parsing for NOTE program headers and add a new NOTE type >>> (NT_GNU_EXEC_FLAGS), though notes tend to be strings... >>> >>> - Add a new Program Header (GNU_EXEC_FLAGS), which is similar to how >>> GNU_STACK and GNU_RELRO were handled. This could sort of be like NOTE >>> except just lots of bit flags. >>> >>> - Use a filesystem xattr. This is fragile, in the case of copying >>> binaries between systems or filesystems. >>> >>> Thoughts? >>> >>> >> >> Why don't you use NT_GNU_PROPERTY_TYPE_0? > > Ah, interesting. I hadn't seen this before. Docs I found were: > https://github.com/hjl-tools/linux-abi/commit/a24f6898c4172e09b2e476ae9f160621528a1d92 > > \item[pr_datasz] The size of the \code{pr_data} field. A 4-byte > integer in the format of the target processor. > \item[pr_data] The program property descriptor. An array of 4-byte > integers in 32-bit object or 8-byte integers in 64-bit objects, in > the format of the target processor. > > Is pr_data length always a multiple of 4 (or 8)? I found this language
Yes.
> confusing, given that pr_datasz doesn't mention this. > > Also, given the definition, should the kernel examine these, or should > it remain limited to the runtimer loader?
Both kernel and run-time loaders should check it. I am working on static PIE, which is loaded by kernel.
> If the kernel should, would it be better to add > GNU_PROPERTY_EXEC_FLAGS, for future bits, or should it be something > like GNU_PROPERTY_NO_COPY_ON_PROTECTED with a pr_datasz == 0?
Please use bits. Is this an output only bit? Will it appear in an input file?
> (And should the kernel already be parsing GNU_PROPERTY_STACK_SIZE?) >
Kernel should.
-- H.J.
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