Re: git: 64ba1f4cf3a6 - main - rtld: Implement LD_SHOW_AUXV
Date: Sat, 13 Nov 2021 17:57:56 UTC
Jess
> 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.
>
> Also the table itself is brittle, there’s nothing checking that the
> order perfectly matches up with the defines in the header. Why not use
> designated initialisers to ensure that the right values are in the
> right entries (and handle the possibility that name might be NULL)?
Scratch that second part, I missed the [at] = in the macro.
Jess