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Message-ID: <20c44e3d-2981-c6cf-f6b8-cc5bfd2fa149@intel.com>
Date: Tue, 27 Sep 2016 15:38:36 -0700
From: "LeMay, Michael" <michael.lemay@...el.com>
To: "musl@...ts.openwall.com" <musl@...ts.openwall.com>
Subject: [RFC PATCH 6/7] support dynamic linking with segmentation-hardened
SafeStack
This patch splits the third stage of dynamic linking around the
initialization of segmentation-hardened SafeStack and adds other
aspects of support for that.
Signed-off-by: Michael LeMay <michael.lemay@...el.com>
---
ldso/dlstart.c | 23 +++++++++++++++++++++--
ldso/dynlink.c | 44 ++++++++++++++++++++++++++++++++++++--------
2 files changed, 57 insertions(+), 10 deletions(-)
diff --git a/ldso/dlstart.c b/ldso/dlstart.c
index 4dbe178..53d2295 100644
--- a/ldso/dlstart.c
+++ b/ldso/dlstart.c
@@ -17,8 +17,14 @@
*(fp) = static_func_ptr; } while(0)
#endif
-__attribute__((__visibility__("hidden")))
-void _dlstart_c(size_t *sp, size_t *dynv)
+#if SAFE_STACK
+#define _DLSTART_C _dlstart_c_impl
+#else
+#define _DLSTART_C _dlstart_c
+#endif
+
+__attribute__((__visibility__("hidden"), noinline))
+void _DLSTART_C(size_t *sp, size_t *dynv)
{
size_t i, aux[AUX_CNT], dyn[DYN_CNT];
size_t *rel, rel_size, base;
@@ -146,3 +152,16 @@ void _dlstart_c(size_t *sp, size_t *dynv)
GETFUNCSYM(&dls2, __dls2, base+dyn[DT_PLTGOT]);
dls2((void *)base, sp);
}
+
+#if SAFE_STACK
+
+void __preinit_unsafe_stack(void);
+
+__attribute__((__visibility__("hidden"), no_sanitize("safe-stack")))
+void _dlstart_c(size_t *sp, size_t *dynv)
+{
+ __preinit_unsafe_stack();
+ _DLSTART_C(sp, dynv);
+}
+
+#endif
diff --git a/ldso/dynlink.c b/ldso/dynlink.c
index e458f38..e729ac1 100644
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -1383,21 +1383,27 @@ void __dls2(unsigned char *base, size_t *sp)
else ((stage3_func)laddr(&ldso, dls3_def.sym->st_value))(sp);
}
+__attribute__((noinline))
+_Noreturn void __dls4(size_t *sp, int argc, char **argv, size_t *aux);
+
+#if SAFE_STACK
+void __init_unsafe_stack(void);
+#endif
+
/* Stage 3 of the dynamic linker is called with the dynamic linker/libc
- * fully functional. Its job is to load (if not already loaded) and
- * process dependencies and relocations for the main application and
- * transfer control to its entry point. */
+ * fully functional. Its job is to prepare for syscalls. It also
configures a
+ * thread-local unsafe stack and protects the safe stack with
segmentation if
+ * those features are enabled. */
+#if SAFE_STACK
+__attribute__((no_sanitize("safe-stack")))
+#endif
_Noreturn void __dls3(size_t *sp)
{
- static struct dso app, vdso;
size_t aux[AUX_CNT], *auxv;
size_t i;
- char *env_preload=0;
- size_t vdso_base;
int argc = *sp;
char **argv = (void *)(sp+1);
- char **argv_orig = argv;
char **envp = argv+argc+1;
/* Find aux vector just past environ[] and use it to initialize
@@ -1420,6 +1426,28 @@ _Noreturn void __dls3(size_t *sp)
a_crash();
}
+#if SAFE_STACK
+ __init_unsafe_stack();
+#endif
+
+ __dls4(sp, argc, argv, aux);
+}
+
+/* Stage 4 of the dynamic linker is called with a thread-local unsafe
stack and
+ * the safe stack protected with segmentation if those features are
enabled.
+ * Its job is to load (if not already loaded) and process dependencies and
+ * relocations for the main application and transfer control to its entry
+ * point. */
+
+_Noreturn void __dls4(size_t *sp, int argc, char **argv, size_t *aux)
+{
+ static struct dso app, vdso;
+ size_t i;
+ char *env_preload=0;
+ size_t vdso_base;
+ char **argv_orig = argv;
+ char *execfn;
+
/* Only trust user/env if kernel says we're not suid/sgid */
if (!libc.secure) {
env_path = getenv("LD_LIBRARY_PATH");
@@ -1549,7 +1577,7 @@ _Noreturn void __dls3(size_t *sp)
}
/* Attach to vdso, if provided by the kernel */
- if (search_vec(auxv, &vdso_base, AT_SYSINFO_EHDR)) {
+ if (search_vec(libc.auxv, &vdso_base, AT_SYSINFO_EHDR)) {
Ehdr *ehdr = (void *)vdso_base;
Phdr *phdr = vdso.phdr = (void *)(vdso_base + ehdr->e_phoff);
vdso.phnum = ehdr->e_phnum;
--
2.7.4
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