RISC-V: Fix IFUNC resolver cannot access gp pointer

In some cases, an IFUNC resolver may need to access the gp pointer to
access global variables. Such an object may have l_relocated == 0 at
this time. In this case, an IFUNC resolver will fail to access a global
variable and cause a SIGSEGV.

This patch fixes this issue by relaxing the check of l_relocated in
elf_machine_runtime_setup, but added a check for SHARED case to avoid
using this code in static-linked executables. Such object have already
set up the gp pointer in load_gp function and l->l_scope will be NULL if
it is a pie object. So if we use these code to set up the gp pointer
again for static-pie, it will causing a SIGSEGV in glibc as original bug
on BZ #31317.

I have also reproduced and checked BZ #31317 using the mold commit
bed5b1731b ("illumos: Treat absolute symbols specially"), this patch can
fix the issue.

Also, we used the wrong gp pointer previously because ref->st_value is
not the relocated address but just the offset from the base address of
ELF. An edge case may happen if we reference gp pointer in a IFUNC
resolver in a PIE object, but it will not happen in compiler-generated
codes since -pie will disable relax to gp. In this case, the GP will be
initialized incorrectly since the ref->st_value is not the address after
relocation. This patch fixes this issue by adding the l->l_addr to
ref->st_value to get the relocated address for the gp pointer. We don't
use SYMBOL_ADDRESS macro here because __global_pointer$ is a special
symbol that has SHN_ABS type, but it will use PC-relative addressing in
the load_gp function using lla.

Closes: BZ #32269
Fixes: 96d1b9ac23 ("RISC-V: Fix the static-PIE non-relocated object check")

Co-authored-by: Vivian Wang <dramforever@live.com>
Signed-off-by: Yangyu Chen <cyy@cyyself.name>

1 files changed, 11 insertions, 6 deletions

diff --git a/sysdeps/riscv/dl-machine.h b/sysdeps/riscv/dl-machine.h
index a30892f..dcc3e08 100644
--- a/sysdeps/riscv/dl-machine.h
+++ b/sysdeps/riscv/dl-machine.h
@@ -348,7 +348,8 @@ elf_machine_runtime_setup (struct link_map *l, struct r_scope_elem *scope[],
       gotplt[1] = (ElfW(Addr)) l;
     }
 
-  if (l->l_type == lt_executable && l->l_relocated)
+#ifdef SHARED
+  if (l->l_type == lt_executable)
     {
       /* The __global_pointer$ may not be defined by the linker if the
 	 $gp register does not be used to access the global variable
@@ -362,13 +363,17 @@ elf_machine_runtime_setup (struct link_map *l, struct r_scope_elem *scope[],
       _dl_lookup_symbol_x ("__global_pointer$", l, &ref,
 			   l->l_scope, NULL, 0, 0, NULL);
       if (ref)
-        asm (
-          "mv gp, %0\n"
-          :
-          : "r" (ref->st_value)
-        );
+	asm (
+	  "mv gp, %0\n"
+	  :
+	  : "r" (ref->st_value + l->l_addr)
+	  /* Don't use SYMBOL_ADDRESS here since __global_pointer$
+	     can be SHN_ABS type, but we need the address relative to
+	     PC, not the absolute address.  */
+	);
     }
 #endif
+#endif
   return lazy;
 }