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V2 Audit bind symbols when no further auditing is required

Message ID 1437079869-27865-1-git-send-email-woodard@redhat.com
State New
Headers show

Commit Message

Ben Woodard July 16, 2015, 8:51 p.m. UTC
In the case where no audit library is interested in a
particular symbol, go ahead and finalize its binding. This improves
performance for cases where an audit library only needs to track one trip
through the PLT and returns peformance to that of a normally lazily bound
symbol. Audit libraries can signal their lack of interest in a symbol by
setting both LA_SYMB_NOPLTENTER and LA_SYMB_NOPLTEXIT in the flags parameter
of la_symbind() or la_pltenter(). If multiple audit libraries are loaded and
they don't all agree that the symbol is no further interest, then the symbol
binding will not be finalized.

Signed-off-by: Ben Woodard <woodard@redhat.com>
---
 ChangeLog        |  6 ++++++
 elf/dl-runtime.c | 25 +++++++++++++++++++++----
 elf/link.h       |  1 +
 3 files changed, 28 insertions(+), 4 deletions(-)
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Patch

diff --git a/ChangeLog b/ChangeLog
index ffeb4d3..485f9ee 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -550,6 +550,12 @@ 
 	* nscd/nscd-client.h (__nscd_acquire_maplock): Use atomic_spin_nop
 	instead of atomic_delay.
 
+2015-06-29  Ben Woodard <woodard@redhat.com>
+
+	* elf/link.h add LA_FLG_NOBIND
+	* elf/dl-runtime.c If no auditing libraries are interested in the
+	PLT entry/exit of a particular symbol, go ahead and finalize it.
+
 2015-06-29  Joseph Myers  <joseph@codesourcery.com>
 
 	[BZ #18613]
diff --git a/elf/dl-runtime.c b/elf/dl-runtime.c
index bd9a1b1..c76d53f 100644
--- a/elf/dl-runtime.c
+++ b/elf/dl-runtime.c
@@ -182,10 +182,21 @@  _dl_profile_fixup (
 
   /* This is the address in the array where we store the result of previous
      relocations.  */
-  struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
+  struct reloc_result reloc_result_value;
+  struct reloc_result *reloc_result;
+  if (l->l_reloc_result)
+    reloc_result = &l->l_reloc_result[reloc_index];
+  else
+    {
+      memset( &reloc_result_value, '\0', sizeof(reloc_result_value));
+      reloc_result = &reloc_result_value;
+    }
   DL_FIXUP_VALUE_TYPE *resultp = &reloc_result->addr;
 
   DL_FIXUP_VALUE_TYPE value = *resultp;
+  const PLTREL *const reloc
+    = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
+  lookup_t result;
   if (DL_FIXUP_VALUE_CODE_ADDR (value) == 0)
     {
       /* This is the first time we have to relocate this object.  */
@@ -193,11 +204,8 @@  _dl_profile_fixup (
 	= (const void *) D_PTR (l, l_info[DT_SYMTAB]);
       const char *strtab = (const char *) D_PTR (l, l_info[DT_STRTAB]);
 
-      const PLTREL *const reloc
-	= (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
       const ElfW(Sym) *refsym = &symtab[ELFW(R_SYM) (reloc->r_info)];
       const ElfW(Sym) *defsym = refsym;
-      lookup_t result;
 
       /* Sanity check that we're really looking at a PLT relocation.  */
       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
@@ -428,6 +436,15 @@  _dl_profile_fixup (
   /* Store the frame size information.  */
   *framesizep = framesize;
 
+  /* If we have auditing libraries and PLT auditing for this symbol has
+     been disabled for all libraries, then go ahead and finalize binding
+     the symbol rather than forcing each call to go through the PLT.  */
+  if ((reloc_result->enterexit & LA_SYMB_NOPLTENTER)
+      && (reloc_result->enterexit & LA_SYMB_NOPLTEXIT))
+    {
+      void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
+      return elf_machine_fixup_plt (l, result, reloc, rel_addr, value);
+    }
   (*mcount_fct) (retaddr, DL_FIXUP_VALUE_CODE_ADDR (value));
 
   return value;
diff --git a/elf/link.h b/elf/link.h
index eaca802..5baf56d 100644
--- a/elf/link.h
+++ b/elf/link.h
@@ -120,6 +120,7 @@  enum
 /* Values for la_objopen return value.  */
 enum
   {
+    LA_FLG_NOBIND = 0x00,	/* Don't audit symbols from this object.  */
     LA_FLG_BINDTO = 0x01,	/* Audit symbols bound to this object.  */
     LA_FLG_BINDFROM = 0x02	/* Audit symbols bound from this object.  */
   };