Re: git: 64ba1f4cf3a6 - main - rtld: Implement LD_SHOW_AUXV

Reply: Jessica Clarke : "Re: git: 64ba1f4cf3a6 - main - rtld: Implement LD_SHOW_AUXV"
In reply to: Konstantin Belousov : "Re: git: 64ba1f4cf3a6 - main - rtld: Implement LD_SHOW_AUXV"
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From: Konstantin Belousov <kostikbel_at_gmail.com>
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");
 	}
 }