linux-hardening - [PATCH 2/4] elf: Move note processing after l

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Message-Id: <7b008fd34f802456db3731a043ff56683b569ff7.1604393169.git.szabolcs.nagy@arm.com>
Date:   Tue,  3 Nov 2020 10:26:18 +0000
From:   Szabolcs Nagy <szabolcs.nagy@....com>
To:     libc-alpha@...rceware.org
Cc:     Jeremy Linton <jeremy.linton@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Brown <broonie@...nel.org>,
        Florian Weimer <fweimer@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Salvatore Mesoraca <s.mesoraca16@...il.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        Topi Miettinen <toiwoton@...il.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kernel-hardening@...ts.openwall.com,
        linux-hardening@...r.kernel.org
Subject: [PATCH 2/4] elf: Move note processing after l_phdr is updated [BZ #26831]

Program headers are processed in two pass: after the first pass
load segments are mmapped so in the second pass target specific
note processing logic can access the notes.

The second pass is moved later so various link_map fields are
set up that may be useful for note processing such as l_phdr.
---
 elf/dl-load.c | 30 +++++++++++++++---------------
 1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/elf/dl-load.c b/elf/dl-load.c
index ceaab7f18e..673cf960a0 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -1259,21 +1259,6 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
 				  maplength, has_holes, loader);
     if (__glibc_unlikely (errstring != NULL))
       goto call_lose;
-
-    /* Process program headers again after load segments are mapped in
-       case processing requires accessing those segments.  Scan program
-       headers backward so that PT_NOTE can be skipped if PT_GNU_PROPERTY
-       exits.  */
-    for (ph = &phdr[l->l_phnum]; ph != phdr; --ph)
-      switch (ph[-1].p_type)
-	{
-	case PT_NOTE:
-	  _dl_process_pt_note (l, fd, &ph[-1]);
-	  break;
-	case PT_GNU_PROPERTY:
-	  _dl_process_pt_gnu_property (l, fd, &ph[-1]);
-	  break;
-	}
   }
 
   if (l->l_ld == 0)
@@ -1481,6 +1466,21 @@ cannot enable executable stack as shared object requires");
     /* Assign the next available module ID.  */
     l->l_tls_modid = _dl_next_tls_modid ();
 
+  /* Process program headers again after load segments are mapped in
+     case processing requires accessing those segments.  Scan program
+     headers backward so that PT_NOTE can be skipped if PT_GNU_PROPERTY
+     exits.  */
+  for (ph = &l->l_phdr[l->l_phnum]; ph != l->l_phdr; --ph)
+    switch (ph[-1].p_type)
+      {
+      case PT_NOTE:
+	_dl_process_pt_note (l, fd, &ph[-1]);
+	break;
+      case PT_GNU_PROPERTY:
+	_dl_process_pt_gnu_property (l, fd, &ph[-1]);
+	break;
+      }
+
 #ifdef DL_AFTER_LOAD
   DL_AFTER_LOAD (l);
 #endif
-- 
2.17.1