Re: git: 64ba1f4cf3a6 - main - rtld: Implement LD_SHOW_AUXV
Date: Sat, 13 Nov 2021 19:06:37 UTC
On Sat, Nov 13, 2021 at 08:59:00PM +0200, Konstantin Belousov wrote: > On Sat, Nov 13, 2021 at 06:29:24PM +0000, Jessica Clarke wrote: > > On 13 Nov 2021, at 17:57, Jessica Clarke <jrtc27@FreeBSD.org> wrote: > > > > > > On 13 Nov 2021, at 17:54, Jessica Clarke <jrtc27@FreeBSD.org> wrote: > > >> > > >> On 13 Nov 2021, at 17:33, Konstantin Belousov <kib@FreeBSD.org> wrote: > > >>> > > >>> The branch main has been updated by kib: > > >>> > > >>> URL: https://cgit.FreeBSD.org/src/commit/?id=64ba1f4cf3a6847a1dacf4bab0409d94898fa168 > > >>> > > >>> commit 64ba1f4cf3a6847a1dacf4bab0409d94898fa168 > > >>> Author: Konstantin Belousov <kib@FreeBSD.org> > > >>> AuthorDate: 2021-11-13 01:18:13 +0000 > > >>> Commit: Konstantin Belousov <kib@FreeBSD.org> > > >>> CommitDate: 2021-11-13 17:33:13 +0000 > > >>> > > >>> rtld: Implement LD_SHOW_AUXV > > >>> > > >>> It dumps auxv as seen by interpreter, right before starting any user > > >>> code. > > >>> > > >>> Copied from: glibc > > >>> Sponsored by: The FreeBSD Foundation > > >>> MFC after: 1 week > > >>> --- > > >>> libexec/rtld-elf/rtld.1 | 7 +++++- > > >>> libexec/rtld-elf/rtld.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++ > > >>> 2 files changed, 73 insertions(+), 1 deletion(-) > > >>> > > >>> diff --git a/libexec/rtld-elf/rtld.1 b/libexec/rtld-elf/rtld.1 > > >>> index 187dc105667a..66aa2bdabd17 100644 > > >>> --- a/libexec/rtld-elf/rtld.1 > > >>> +++ b/libexec/rtld-elf/rtld.1 > > >>> @@ -28,7 +28,7 @@ > > >>> .\" > > >>> .\" $FreeBSD$ > > >>> .\" > > >>> -.Dd August 15, 2021 > > >>> +.Dd November 13, 2021 > > >>> .Dt RTLD 1 > > >>> .Os > > >>> .Sh NAME > > >>> @@ -309,6 +309,11 @@ will process the filtee dependencies of the loaded objects immediately, > > >>> instead of postponing it until required. > > >>> Normally, the filtees are opened at the time of the first symbol resolution > > >>> from the filter object. > > >>> +.It Ev LD_SHOW_AUXV > > >>> +If set, causes > > >>> +.Nm > > >>> +to dump content of the aux vector to standard output, before passing > > >>> +control to any user code. > > >>> .El > > >>> .Sh DIRECT EXECUTION MODE > > >>> .Nm > > >>> diff --git a/libexec/rtld-elf/rtld.c b/libexec/rtld-elf/rtld.c > > >>> index c173c5a6e22e..0475134b0d96 100644 > > >>> --- a/libexec/rtld-elf/rtld.c > > >>> +++ b/libexec/rtld-elf/rtld.c > > >>> @@ -104,6 +104,7 @@ static Obj_Entry *dlopen_object(const char *name, int fd, Obj_Entry *refobj, > > >>> static Obj_Entry *do_load_object(int, const char *, char *, struct stat *, int); > > >>> static int do_search_info(const Obj_Entry *obj, int, struct dl_serinfo *); > > >>> static bool donelist_check(DoneList *, const Obj_Entry *); > > >>> +static void dump_auxv(Elf_Auxinfo **aux_info); > > >>> static void errmsg_restore(struct dlerror_save *); > > >>> static struct dlerror_save *errmsg_save(void); > > >>> static void *fill_search_info(const char *, size_t, void *); > > >>> @@ -364,6 +365,7 @@ enum { > > >>> LD_TRACE_LOADED_OBJECTS_FMT1, > > >>> LD_TRACE_LOADED_OBJECTS_FMT2, > > >>> LD_TRACE_LOADED_OBJECTS_ALL, > > >>> + LD_SHOW_AUXV, > > >>> }; > > >>> > > >>> struct ld_env_var_desc { > > >>> @@ -396,6 +398,7 @@ static struct ld_env_var_desc ld_env_vars[] = { > > >>> LD_ENV_DESC(TRACE_LOADED_OBJECTS_FMT1, false), > > >>> LD_ENV_DESC(TRACE_LOADED_OBJECTS_FMT2, false), > > >>> LD_ENV_DESC(TRACE_LOADED_OBJECTS_ALL, false), > > >>> + LD_ENV_DESC(SHOW_AUXV, false), > > >>> }; > > >>> > > >>> static const char * > > >>> @@ -857,6 +860,9 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp) > > >>> if (rtld_verify_versions(&list_main) == -1 && !ld_tracing) > > >>> rtld_die(); > > >>> > > >>> + if (ld_get_env_var(LD_SHOW_AUXV) != NULL) > > >>> + dump_auxv(aux_info); > > >>> + > > >>> if (ld_tracing) { /* We're done */ > > >>> trace_loaded_objects(obj_main); > > >>> exit(0); > > >>> @@ -6058,6 +6064,67 @@ print_usage(const char *argv0) > > >>> " <args> Arguments to the executed process\n", argv0); > > >>> } > > >>> > > >>> +#define AUXFMT(at, xfmt) [at] = { .name = #at, .fmt = xfmt } > > >>> +static const struct auxfmt { > > >>> + const char *name; > > >>> + const char *fmt; > > >>> +} auxfmts[] = { > > >>> + AUXFMT(AT_NULL, NULL), > > >>> + AUXFMT(AT_IGNORE, NULL), > > >>> + AUXFMT(AT_EXECFD, "%d"), > > >>> + AUXFMT(AT_PHDR, "%p"), > > >>> + AUXFMT(AT_PHENT, "%u"), > > >>> + AUXFMT(AT_PHNUM, "%u"), > > >>> + AUXFMT(AT_PAGESZ, "%u"), > > >>> + AUXFMT(AT_BASE, "%#lx"), > > >>> + AUXFMT(AT_FLAGS, "%#lx"), > > >>> + AUXFMT(AT_ENTRY, "%p"), > > >>> + AUXFMT(AT_NOTELF, NULL), > > >>> + AUXFMT(AT_UID, "%d"), > > >>> + AUXFMT(AT_EUID, "%d"), > > >>> + AUXFMT(AT_GID, "%d"), > > >>> + AUXFMT(AT_EGID, "%d"), > > >>> + AUXFMT(AT_EXECPATH, "%s"), > > >>> + AUXFMT(AT_CANARY, "%p"), > > >>> + AUXFMT(AT_CANARYLEN, "%u"), > > >>> + AUXFMT(AT_OSRELDATE, "%u"), > > >>> + AUXFMT(AT_NCPUS, "%u"), > > >>> + AUXFMT(AT_PAGESIZES, "%p"), > > >>> + AUXFMT(AT_PAGESIZESLEN, "%u"), > > >>> + AUXFMT(AT_TIMEKEEP, "%p"), > > >>> + AUXFMT(AT_STACKPROT, "%#x"), > > >>> + AUXFMT(AT_EHDRFLAGS, "%#lx"), > > >>> + AUXFMT(AT_HWCAP, "%#lx"), > > >>> + AUXFMT(AT_HWCAP2, "%#lx"), > > >>> + AUXFMT(AT_BSDFLAGS, "%#lx"), > > >>> + AUXFMT(AT_ARGC, "%u"), > > >>> + AUXFMT(AT_ARGV, "%p"), > > >>> + AUXFMT(AT_ENVC, "%p"), > > >>> + AUXFMT(AT_ENVV, "%p"), > > >>> + AUXFMT(AT_PS_STRINGS, "%p"), > > >>> + AUXFMT(AT_FXRNG, "%p"), > > >>> +}; > > >>> + > > >>> +static void > > >>> +dump_auxv(Elf_Auxinfo **aux_info) > > >>> +{ > > >>> + Elf_Auxinfo *auxp; > > >>> + const struct auxfmt *fmt; > > >>> + int i; > > >>> + > > >>> + for (i = 0; i < AT_COUNT; i++) { > > >>> + auxp = aux_info[i]; > > >>> + if (auxp == NULL) > > >>> + continue; > > >>> + fmt = &auxfmts[i]; > > >>> + if (fmt->fmt == NULL) > > >>> + continue; > > >>> + rtld_fdprintf(STDOUT_FILENO, "%s:\t", fmt->name); > > >>> + rtld_fdprintfx(STDOUT_FILENO, fmt->fmt, auxp->a_un.a_ptr); > > >>> + rtld_fdprintf(STDOUT_FILENO, "\n"); > > >> > > >> This is undefined behaviour, breaks CHERI, and totally unnecessary. You > > >> have a handful of cases here, just make an enum and have separate > > >> rtld_fdprintf calls. > > > > In particular, ignoring CHERI, unsigned ints are sign-extended to 64 > > bits on MIPS and RISC-V. Thus by passing a 64-bit value but using a %u, > > you are violating the calling convention. I can’t currently get GCC or > > Clang to exploit the fact that varargs arguments are sign-extended, but > > on MIPS, and RISC-V GCC (Clang is currently stupid and round-trips via > > memory even when the va_arg calls have no branching surrounding them, > > rather than just grabbing from the register) there is a redundant > > sext.w that can legally be optimised out, but would be broken by this > > calling convention violation. > I might understand the argument that all non-pointer formats for auxv > should be longs, i.e. %lu/%ld/%lx, but this is the only problem I see > there. We do rely on having specific representations for addresses and > longs, and a low-level component as rtld has full rights to exercise > this fact, same as VM subsystem or memory allocators. > > In fact ELF spec exercises this as well. > Our arches are either ILP32 or LP64. > > > > > Then CHERI makes it worse because a_ptr and a_val do not have the same > > representation, although in practice I think passing a_ptr and nothing > > further does end up working on CHERI-RISC-V and Morello, just not > > CHERI-MIPS due to being big-endian. Ok, the following should be enough for CHERI, right? diff --git a/libexec/rtld-elf/rtld.c b/libexec/rtld-elf/rtld.c index 0475134b0d96..cf467ae7aacd 100644 --- a/libexec/rtld-elf/rtld.c +++ b/libexec/rtld-elf/rtld.c @@ -6071,33 +6071,33 @@ static const struct auxfmt { } auxfmts[] = { AUXFMT(AT_NULL, NULL), AUXFMT(AT_IGNORE, NULL), - AUXFMT(AT_EXECFD, "%d"), + AUXFMT(AT_EXECFD, "%ld"), AUXFMT(AT_PHDR, "%p"), - AUXFMT(AT_PHENT, "%u"), - AUXFMT(AT_PHNUM, "%u"), - AUXFMT(AT_PAGESZ, "%u"), + AUXFMT(AT_PHENT, "%lu"), + AUXFMT(AT_PHNUM, "%lu"), + AUXFMT(AT_PAGESZ, "%lu"), AUXFMT(AT_BASE, "%#lx"), AUXFMT(AT_FLAGS, "%#lx"), AUXFMT(AT_ENTRY, "%p"), AUXFMT(AT_NOTELF, NULL), - AUXFMT(AT_UID, "%d"), - AUXFMT(AT_EUID, "%d"), - AUXFMT(AT_GID, "%d"), - AUXFMT(AT_EGID, "%d"), + AUXFMT(AT_UID, "%ld"), + AUXFMT(AT_EUID, "%ld"), + AUXFMT(AT_GID, "%ld"), + AUXFMT(AT_EGID, "%ld"), AUXFMT(AT_EXECPATH, "%s"), AUXFMT(AT_CANARY, "%p"), - AUXFMT(AT_CANARYLEN, "%u"), - AUXFMT(AT_OSRELDATE, "%u"), - AUXFMT(AT_NCPUS, "%u"), + AUXFMT(AT_CANARYLEN, "%lu"), + AUXFMT(AT_OSRELDATE, "%lu"), + AUXFMT(AT_NCPUS, "%lu"), AUXFMT(AT_PAGESIZES, "%p"), - AUXFMT(AT_PAGESIZESLEN, "%u"), + AUXFMT(AT_PAGESIZESLEN, "%lu"), AUXFMT(AT_TIMEKEEP, "%p"), - AUXFMT(AT_STACKPROT, "%#x"), + AUXFMT(AT_STACKPROT, "%#lx"), AUXFMT(AT_EHDRFLAGS, "%#lx"), AUXFMT(AT_HWCAP, "%#lx"), AUXFMT(AT_HWCAP2, "%#lx"), AUXFMT(AT_BSDFLAGS, "%#lx"), - AUXFMT(AT_ARGC, "%u"), + AUXFMT(AT_ARGC, "%lu"), AUXFMT(AT_ARGV, "%p"), AUXFMT(AT_ENVC, "%p"), AUXFMT(AT_ENVV, "%p"), @@ -6105,6 +6105,15 @@ static const struct auxfmt { AUXFMT(AT_FXRNG, "%p"), }; +static bool +is_ptr_fmt(const char *fmt) +{ + char last; + + last = fmt[strlen(fmt) - 1]; + return (last == 'p' || last == 's'); +} + static void dump_auxv(Elf_Auxinfo **aux_info) { @@ -6120,7 +6129,8 @@ dump_auxv(Elf_Auxinfo **aux_info) if (fmt->fmt == NULL) continue; rtld_fdprintf(STDOUT_FILENO, "%s:\t", fmt->name); - rtld_fdprintfx(STDOUT_FILENO, fmt->fmt, auxp->a_un.a_ptr); + rtld_fdprintfx(STDOUT_FILENO, fmt->fmt, is_ptr_fmt(fmt->fmt) ? + auxp->a_un.a_ptr : auxp->a_un.a_val); rtld_fdprintf(STDOUT_FILENO, "\n"); } }