| Message ID | 20150929231649.GA7821@brightrain.aerifal.cx (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Ping. On Tue, Sep 29, 2015 at 07:16:49PM -0400, Rich Felker wrote: > From: Rich Felker <dalias@libc.org> > > The ELF binary loader in binfmt_elf.c requires an MMU, making it > impossible to use regular ELF binaries on NOMMU archs. However, the > FDPIC ELF loader in binfmt_elf_fdpic.c is fully capable as a loader > for plain ELF, which requires constant displacements between LOAD > segments, since it already supports FDPIC ELF files flagged as needing > constant displacement. > > This patch adjusts the FDPIC ELF loader to accept non-FDPIC ELF files > on NOMMU archs. They are treated identically to FDPIC ELF files with > the constant-displacement flag bit set, except for personality, which > must match the ABI of the program being loaded; the PER_LINUX_FDPIC > personality controls how the kernel interprets function pointers > passed to sigaction. > > Files that do not set a stack size requirement explicitly are given a > default stack size (matching the amount of committed stack the normal > ELF loader for MMU archs would give them) rather than being rejected; > this is necessary because plain ELF files generally do not declare > stack requirements in theit program headers. > > Only ET_DYN (PIE) format ELF files are supported, since loading at a > fixed virtual address is not possible on NOMMU. > > Signed-off-by: Rich Felker <dalias@libc.org> > --- > > This patch was developed and tested on J2 (SH2-compatible) but should > be usable immediately on all archs where binfmt_elf_fdpic is > available. Moreover, by providing dummy definitions of the > elf_check_fdpic() and elf_check_const_displacement() macros for archs > which lack an FDPIC ABI, it should be possible to enable building of > binfmt_elf_fdpic on all other NOMMU archs and thereby give them ELF > binary support, but I have not yet tested this. > > The motivation for using binfmt_elf_fdpic.c rather than adapting > binfmt_elf.c to NOMMU is that the former already has all the necessary > code to work properly on NOMMU and has already received widespread > real-world use and testing. I hope this is not controversial. > > I'm not really happy with having to unset the FDPIC_FUNCPTRS > personality bit when loading non-FDPIC ELF. This bit should really > reset automatically on execve, since otherwise, executing non-ELF > binaries (e.g. bFLT) from an FDPIC process will leave the personality > in the wrong state and severely break signal handling. But that's a > separate, existing bug and I don't know the right place to fix it. > > > > --- fs/binfmt_elf_fdpic.c.orig 2015-09-29 22:13:06.716412478 +0000 > +++ fs/binfmt_elf_fdpic.c 2015-09-29 22:38:24.122986621 +0000 > @@ -103,19 +103,36 @@ > core_initcall(init_elf_fdpic_binfmt); > module_exit(exit_elf_fdpic_binfmt); > > -static int is_elf_fdpic(struct elfhdr *hdr, struct file *file) > +static int is_elf(struct elfhdr *hdr, struct file *file) > { > if (memcmp(hdr->e_ident, ELFMAG, SELFMAG) != 0) > return 0; > if (hdr->e_type != ET_EXEC && hdr->e_type != ET_DYN) > return 0; > - if (!elf_check_arch(hdr) || !elf_check_fdpic(hdr)) > + if (!elf_check_arch(hdr)) > return 0; > if (!file->f_op->mmap) > return 0; > return 1; > } > > +#ifndef elf_check_fdpic > +#define elf_check_fdpic(x) 0 > +#endif > + > +#ifndef elf_check_const_displacement > +#define elf_check_const_displacement(x) 0 > +#endif > + > +static int is_constdisp(struct elfhdr *hdr) > +{ > + if (!elf_check_fdpic(hdr)) > + return 1; > + if (elf_check_const_displacement(hdr)) > + return 1; > + return 0; > +} > + > /*****************************************************************************/ > /* > * read the program headers table into memory > @@ -191,8 +208,16 @@ > > /* check that this is a binary we know how to deal with */ > retval = -ENOEXEC; > - if (!is_elf_fdpic(&exec_params.hdr, bprm->file)) > + if (!is_elf(&exec_params.hdr, bprm->file)) > + goto error; > +#ifdef CONFIG_MMU > + /* binfmt_elf handles non-fdpic elf except on nommu */ > + if (!elf_check_fdpic(&exec_params.hdr)) > + goto error; > +#else > + if (exec_params.hdr.e_type != ET_DYN) > goto error; > +#endif > > /* read the program header table */ > retval = elf_fdpic_fetch_phdrs(&exec_params, bprm->file); > @@ -269,13 +294,13 @@ > > } > > - if (elf_check_const_displacement(&exec_params.hdr)) > + if (is_constdisp(&exec_params.hdr)) > exec_params.flags |= ELF_FDPIC_FLAG_CONSTDISP; > > /* perform insanity checks on the interpreter */ > if (interpreter_name) { > retval = -ELIBBAD; > - if (!is_elf_fdpic(&interp_params.hdr, interpreter)) > + if (!is_elf(&interp_params.hdr, interpreter)) > goto error; > > interp_params.flags = ELF_FDPIC_FLAG_PRESENT; > @@ -306,9 +331,9 @@ > > retval = -ENOEXEC; > if (stack_size == 0) > - goto error; > + stack_size = 131072UL; /* same as exec.c's default commit */ > > - if (elf_check_const_displacement(&interp_params.hdr)) > + if (is_constdisp(&interp_params.hdr)) > interp_params.flags |= ELF_FDPIC_FLAG_CONSTDISP; > > /* flush all traces of the currently running executable */ > @@ -319,7 +344,10 @@ > /* there's now no turning back... the old userspace image is dead, > * defunct, deceased, etc. > */ > - set_personality(PER_LINUX_FDPIC); > + if (elf_check_fdpic(&exec_params.hdr)) > + set_personality(PER_LINUX_FDPIC); > + else > + set_personality(PER_LINUX); > if (elf_read_implies_exec(&exec_params.hdr, executable_stack)) > current->personality |= READ_IMPLIES_EXEC; > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
--- fs/binfmt_elf_fdpic.c.orig 2015-09-29 22:13:06.716412478 +0000 +++ fs/binfmt_elf_fdpic.c 2015-09-29 22:38:24.122986621 +0000 @@ -103,19 +103,36 @@ core_initcall(init_elf_fdpic_binfmt); module_exit(exit_elf_fdpic_binfmt); -static int is_elf_fdpic(struct elfhdr *hdr, struct file *file) +static int is_elf(struct elfhdr *hdr, struct file *file) { if (memcmp(hdr->e_ident, ELFMAG, SELFMAG) != 0) return 0; if (hdr->e_type != ET_EXEC && hdr->e_type != ET_DYN) return 0; - if (!elf_check_arch(hdr) || !elf_check_fdpic(hdr)) + if (!elf_check_arch(hdr)) return 0; if (!file->f_op->mmap) return 0; return 1; } +#ifndef elf_check_fdpic +#define elf_check_fdpic(x) 0 +#endif + +#ifndef elf_check_const_displacement +#define elf_check_const_displacement(x) 0 +#endif + +static int is_constdisp(struct elfhdr *hdr) +{ + if (!elf_check_fdpic(hdr)) + return 1; + if (elf_check_const_displacement(hdr)) + return 1; + return 0; +} + /*****************************************************************************/ /* * read the program headers table into memory @@ -191,8 +208,16 @@ /* check that this is a binary we know how to deal with */ retval = -ENOEXEC; - if (!is_elf_fdpic(&exec_params.hdr, bprm->file)) + if (!is_elf(&exec_params.hdr, bprm->file)) + goto error; +#ifdef CONFIG_MMU + /* binfmt_elf handles non-fdpic elf except on nommu */ + if (!elf_check_fdpic(&exec_params.hdr)) + goto error; +#else + if (exec_params.hdr.e_type != ET_DYN) goto error; +#endif /* read the program header table */ retval = elf_fdpic_fetch_phdrs(&exec_params, bprm->file); @@ -269,13 +294,13 @@ } - if (elf_check_const_displacement(&exec_params.hdr)) + if (is_constdisp(&exec_params.hdr)) exec_params.flags |= ELF_FDPIC_FLAG_CONSTDISP; /* perform insanity checks on the interpreter */ if (interpreter_name) { retval = -ELIBBAD; - if (!is_elf_fdpic(&interp_params.hdr, interpreter)) + if (!is_elf(&interp_params.hdr, interpreter)) goto error; interp_params.flags = ELF_FDPIC_FLAG_PRESENT; @@ -306,9 +331,9 @@ retval = -ENOEXEC; if (stack_size == 0) - goto error; + stack_size = 131072UL; /* same as exec.c's default commit */ - if (elf_check_const_displacement(&interp_params.hdr)) + if (is_constdisp(&interp_params.hdr)) interp_params.flags |= ELF_FDPIC_FLAG_CONSTDISP; /* flush all traces of the currently running executable */ @@ -319,7 +344,10 @@ /* there's now no turning back... the old userspace image is dead, * defunct, deceased, etc. */ - set_personality(PER_LINUX_FDPIC); + if (elf_check_fdpic(&exec_params.hdr)) + set_personality(PER_LINUX_FDPIC); + else + set_personality(PER_LINUX); if (elf_read_implies_exec(&exec_params.hdr, executable_stack)) current->personality |= READ_IMPLIES_EXEC;