stand: Improve error handling when loading ELF files

Previously all the 'goto out' statements after the image was loaded into
memory returned success rather than an error.  This is despite comments
indicating some of these conditions were in fact errors, and some of
these error conditions (such as missing PT_DYNAMIC) are treated as errors
in the kernel linker.

In addition, when failing to looking up the symbols for the linker
set, those cases returned failure leaking memory (though it's clear
from the original code from commit ca49b3342d1e that only the second
failure was intended to be an actual error).

To avoid more confusion, move the assignment of `ret` to just before
the `out` label so that `goto out` always returns an error.  This is a
more consistent pattern with other code in the tree that tends to use
labels for the error case.

Restructure some other code to avoid a few bogus errors.
Specifically, a symbol table is not required so don't treat lack of a
symbol table as an error.  Also, if the start symbol for the module
metadata linker set is not found, don't treat that as an error either.

Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D58540

1 files changed, 20 insertions, 18 deletions

diff --git a/stand/common/load_elf.c b/stand/common/load_elf.c
index 97467094750c..14fc0893f088 100644
--- a/stand/common/load_elf.c
+++ b/stand/common/load_elf.c
@@ -838,7 +838,6 @@ nosyms:
 	if (module_verbose > MODULE_VERBOSE_SILENT)
 		printf("\n");
 
-	ret = lastaddr - firstaddr;
 	fp->f_addr = firstaddr;
 
 	php = NULL;
@@ -901,25 +900,28 @@ nosyms:
 			break;
 		}
 	}
-	if (ef->hashtab == NULL || ef->symtab == NULL ||
-	    ef->strtab == NULL || ef->strsz == 0)
-		goto out;
-	COPYOUT(ef->hashtab, &ef->nbuckets, sizeof(ef->nbuckets));
-	COPYOUT(ef->hashtab + 1, &ef->nchains, sizeof(ef->nchains));
-	ef->buckets = ef->hashtab + 2;
-	ef->chains = ef->buckets + ef->nbuckets;
+	if (ef->hashtab != NULL && ef->symtab != NULL &&
+	    ef->strtab != NULL && ef->strsz != 0) {
+		COPYOUT(ef->hashtab, &ef->nbuckets, sizeof(ef->nbuckets));
+		COPYOUT(ef->hashtab + 1, &ef->nchains, sizeof(ef->nchains));
+		ef->buckets = ef->hashtab + 2;
+		ef->chains = ef->buckets + ef->nbuckets;
+	}
 
-	if (__elfN(lookup_symbol)(ef, "__start_set_modmetadata_set", &sym,
-	    STT_NOTYPE) != 0)
-		return 0;
-	p_start = sym.st_value + ef->off;
-	if (__elfN(lookup_symbol)(ef, "__stop_set_modmetadata_set", &sym,
-	    STT_NOTYPE) != 0)
-		return 0;
-	p_end = sym.st_value + ef->off;
+	/* Don't emit a warning if there is no symbol table. */
+	if (ef->buckets != 0 && __elfN(lookup_symbol)(ef,
+	    "__start_set_modmetadata_set", &sym, STT_NOTYPE) == 0) {
+		p_start = sym.st_value + ef->off;
+		if (__elfN(lookup_symbol)(ef, "__stop_set_modmetadata_set",
+		    &sym, STT_NOTYPE) != 0)
+			goto out;
+		p_end = sym.st_value + ef->off;
 
-	if (__elfN(parse_modmetadata)(fp, ef, p_start, p_end) == 0)
-		goto out;
+		if (__elfN(parse_modmetadata)(fp, ef, p_start, p_end) != 0)
+			goto out;
+	}
+
+	ret = lastaddr - firstaddr;
 
 out:
 	if (dp)