From ca8c8dc3ebe7a92dd6d7951231769154a0454b52 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Wed, 2 Mar 2016 16:36:24 +0000
Subject: [PATCH] Fix handling of DT_TEXTREL for an object with more than one
 read-only segment.  According to gABI spec, presence of the tag indicates
 that dynamic linker must be prepared to handle relocations against any
 read-only segment, not only the segment which we, somewhat arbitrary,
 declared the text.

For each read-only segment, add write permission before relocs are
processed, and return to the mapping mode requested by the phdr, after
relocs are done.

Reported, tested, and reviewed by:	emaste
PR:	207631
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
---
 libexec/rtld-elf/map_object.c |  3 +-
 libexec/rtld-elf/rtld.c       | 57 ++++++++++++++++++++++++-----------
 libexec/rtld-elf/rtld.h       |  1 +
 3 files changed, 42 insertions(+), 19 deletions(-)

diff --git a/libexec/rtld-elf/map_object.c b/libexec/rtld-elf/map_object.c
index f4f6f4221816..30af4cefddbe 100644
--- a/libexec/rtld-elf/map_object.c
+++ b/libexec/rtld-elf/map_object.c
@@ -39,7 +39,6 @@
 #include "rtld.h"
 
 static Elf_Ehdr *get_elf_header(int, const char *, const struct stat *);
-static int convert_prot(int);	/* Elf flags -> mmap protection */
 static int convert_flags(int); /* Elf flags -> mmap flags */
 
 /*
@@ -445,7 +444,7 @@ obj_new(void)
  * Given a set of ELF protection flags, return the corresponding protection
  * flags for MMAP.
  */
-static int
+int
 convert_prot(int elfflags)
 {
     int prot = 0;
diff --git a/libexec/rtld-elf/rtld.c b/libexec/rtld-elf/rtld.c
index 912358c0c1d1..6a405c30f508 100644
--- a/libexec/rtld-elf/rtld.c
+++ b/libexec/rtld-elf/rtld.c
@@ -2626,6 +2626,40 @@ relocate_object_dag(Obj_Entry *root, bool bind_now, Obj_Entry *rtldobj,
 	return (error);
 }
 
+/*
+ * Prepare for, or clean after, relocating an object marked with
+ * DT_TEXTREL or DF_TEXTREL.  Before relocating, all read-only
+ * segments are remapped read-write.  After relocations are done, the
+ * segment's permissions are returned back to the modes specified in
+ * the phdrs.  If any relocation happened, or always for wired
+ * program, COW is triggered.
+ */
+static int
+reloc_textrel_prot(Obj_Entry *obj, bool before)
+{
+	const Elf_Phdr *ph;
+	void *base;
+	size_t l, sz;
+	int prot;
+
+	for (l = obj->phsize / sizeof(*ph), ph = obj->phdr; l > 0;
+	    l--, ph++) {
+		if (ph->p_type != PT_LOAD || (ph->p_flags & PF_W) != 0)
+			continue;
+		base = obj->relocbase + trunc_page(ph->p_vaddr);
+		sz = round_page(ph->p_vaddr + ph->p_filesz) -
+		    trunc_page(ph->p_vaddr);
+		prot = convert_prot(ph->p_flags) | (before ? PROT_WRITE : 0);
+		if (mprotect(base, sz, prot) == -1) {
+			_rtld_error("%s: Cannot write-%sable text segment: %s",
+			    obj->path, before ? "en" : "dis",
+			    rtld_strerror(errno));
+			return (-1);
+		}
+	}
+	return (0);
+}
+
 /*
  * Relocate single object.
  * Returns 0 on success, or -1 on failure.
@@ -2648,28 +2682,17 @@ relocate_object(Obj_Entry *obj, bool bind_now, Obj_Entry *rtldobj,
 		return (-1);
 	}
 
-	if (obj->textrel) {
-		/* There are relocations to the write-protected text segment. */
-		if (mprotect(obj->mapbase, obj->textsize,
-		    PROT_READ|PROT_WRITE|PROT_EXEC) == -1) {
-			_rtld_error("%s: Cannot write-enable text segment: %s",
-			    obj->path, rtld_strerror(errno));
-			return (-1);
-		}
-	}
+	/* There are relocations to the write-protected text segment. */
+	if (obj->textrel && reloc_textrel_prot(obj, true) != 0)
+		return (-1);
 
 	/* Process the non-PLT non-IFUNC relocations. */
 	if (reloc_non_plt(obj, rtldobj, flags, lockstate))
 		return (-1);
 
-	if (obj->textrel) {	/* Re-protected the text segment. */
-		if (mprotect(obj->mapbase, obj->textsize,
-		    PROT_READ|PROT_EXEC) == -1) {
-			_rtld_error("%s: Cannot write-protect text segment: %s",
-			    obj->path, rtld_strerror(errno));
-			return (-1);
-		}
-	}
+	/* Re-protected the text segment. */
+	if (obj->textrel && reloc_textrel_prot(obj, false) != 0)
+		return (-1);
 
 	/* Set the special PLT or GOT entries. */
 	init_pltgot(obj);
diff --git a/libexec/rtld-elf/rtld.h b/libexec/rtld-elf/rtld.h
index 5fbfb271a3bf..8b7024b841ad 100644
--- a/libexec/rtld-elf/rtld.h
+++ b/libexec/rtld-elf/rtld.h
@@ -385,6 +385,7 @@ void *allocate_module_tls(int index);
 bool allocate_tls_offset(Obj_Entry *obj);
 void free_tls_offset(Obj_Entry *obj);
 const Ver_Entry *fetch_ventry(const Obj_Entry *obj, unsigned long);
+int convert_prot(int elfflags);
 
 /*
  * MD function declarations.