linux-kernel - [PATCH v2 1/6] aarch64: Fix missing BTI protection from dependencies [BZ #26926]

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Date:   Fri, 27 Nov 2020 13:19:43 +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 1/6] aarch64: Fix missing BTI protection from dependencies [BZ #26926]

The _dl_open_check and _rtld_main_check hooks are not called on the
dependencies of a loaded module, so BTI protection was missed on
every module other than the main executable and directly dlopened
libraries.

The fix just iterates over dependencies to enable BTI.

Fixes bug 26926.
---
 sysdeps/aarch64/dl-bti.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/sysdeps/aarch64/dl-bti.c b/sysdeps/aarch64/dl-bti.c
index 196e462520..8f4728adce 100644
--- a/sysdeps/aarch64/dl-bti.c
+++ b/sysdeps/aarch64/dl-bti.c
@@ -51,11 +51,24 @@ enable_bti (struct link_map *map, const char *program)
   return 0;
 }
 
-/* Enable BTI for L if required.  */
+/* Enable BTI for MAP and its dependencies.  */
 
 void
-_dl_bti_check (struct link_map *l, const char *program)
+_dl_bti_check (struct link_map *map, const char *program)
 {
-  if (GLRO(dl_aarch64_cpu_features).bti && l->l_mach.bti)
-    enable_bti (l, program);
+  if (!GLRO(dl_aarch64_cpu_features).bti)
+    return;
+
+  if (map->l_mach.bti)
+    enable_bti (map, program);
+
+  unsigned int i = map->l_searchlist.r_nlist;
+  while (i-- > 0)
+    {
+      struct link_map *l = map->l_initfini[i];
+      if (l->l_init_called)
+	continue;
+      if (l->l_mach.bti)
+	enable_bti (l, program);
+    }
 }
-- 
2.17.1