linux-kernel - [PATCH v2 4/6] elf: Move note processing after l

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Message-Id: <36d457074f389740b45afc4f9c6d124046f8352b.1606319495.git.szabolcs.nagy@arm.com>
Date:   Fri, 27 Nov 2020 13:20:56 +0000
From:   Szabolcs Nagy <szabolcs.nagy@....com>
To:     libc-alpha@...rceware.org
Cc:     Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        Jeremy Linton <jeremy.linton@....com>,
        Mark Brown <broonie@...nel.org>,
        kernel-hardening@...ts.openwall.com,
        Topi Miettinen <toiwoton@...il.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH v2 4/6] elf: Move note processing after l_phdr is updated

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.
The second pass should be before the fd is closed so that is
available.
---
 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 9c71b7562c..b0d65f32cc 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -1268,21 +1268,6 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
 	l->l_map_start = l->l_map_end = 0;
 	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, &ph[-1]);
-	  break;
-	case PT_GNU_PROPERTY:
-	  _dl_process_pt_gnu_property (l, &ph[-1]);
-	  break;
-	}
   }
 
   if (l->l_ld == 0)
@@ -1386,6 +1371,21 @@ cannot enable executable stack as shared object requires");
   if (l->l_tls_initimage != NULL)
     l->l_tls_initimage = (char *) l->l_tls_initimage + l->l_addr;
 
+  /* 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, &ph[-1]);
+	break;
+      case PT_GNU_PROPERTY:
+	_dl_process_pt_gnu_property (l, &ph[-1]);
+	break;
+      }
+
   /* We are done mapping in the file.  We no longer need the descriptor.  */
   if (__glibc_unlikely (__close_nocancel (fd) != 0))
     {
-- 
2.17.1