Messages in this thread | | | From | "H.J. Lu" <> | Date | Sun, 12 Dec 2021 11:30:01 -0800 | Subject | Re: [PATCH] fs/binfmt_elf.c: disallow zero entry point address |
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On Sun, Dec 12, 2021 at 11:15 AM Linus Torvalds <torvalds@linux-foundation.org> wrote: > > On Sun, Dec 12, 2021 at 11:06 AM H.J. Lu <hjl.tools@gmail.com> wrote: > > > > According to the ELF specification, zero entry point value means > > there is no entry point. Such ELF binary doesn't conform to the > > ELF specification. > > Nobody cares about paper specifications. > > All that matters is REALITY. > > So let me quote my email again, since you clearly didn't actually read > it (read that "maybe it's not supposed to work" part): > > > That's not my main worry - what if somebody has a code section with a > > zero vaddr and intentionally put the entry at the beginning? > > > > Maybe it's not supposed to work by some paper standatd, but afaik > > currently it _would_ work. > > I'm not sure this can happen currently (maybe all tools effectively > make it so that the ELF headers etc are part of the loaded image). > > But no, paper specifications have absolutely no meaning if they don't > match realty. > > And the reality is that I don't think we've ever checked e_entry being > zero, which means that maybe people have used it. > > So convince me that the above cannot happen. I'm perfectly willing to > be convinced, but "some random paper standard that we've never > followed" is not the thing to quote. >
On Linux, the start of the first PT_LOAD segment is the ELF header and the address 0 points to the ELF magic bytes which isn't a valid code sequence.
-- H.J.
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