[PATCH v4 06/10] nx: set page permissions for loaded modules.

[Mate Kukri]

For NX, we need to set write and executable permissions on the sections
of grub modules when we load them.

On sections with SHF_ALLOC set, which is typically everything except
.modname and the symbol and string tables, this patch clears the Read
Only flag on sections that have the ELF flag SHF_WRITE set, and clears
the No eXecute flag on sections with SHF_EXECINSTR set.  In all other
cases it sets both flags.

Original-Author: Peter Jones <pjones@redhat.com>
Original-Author: Robbie Harwood <rharwood@redhat.com>
Original-Author: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Mate Kukri <mate.kukri@canonical.com>
---
 grub-core/kern/dl.c | 104 ++++++++++++++++++++++++++++++++++++++------
 include/grub/dl.h   |  46 ++++++++++++++++++++
 2 files changed, 137 insertions(+), 13 deletions(-)

diff --git a/grub-core/kern/dl.c b/grub-core/kern/dl.c
index 8338f7436..3341d78d6 100644
--- a/grub-core/kern/dl.c
+++ b/grub-core/kern/dl.c
@@ -616,25 +616,97 @@ grub_dl_relocate_symbols (grub_dl_t mod, void *ehdr)
        grub_dl_segment_t seg;
        grub_err_t err;
 
-       /* Find the target segment.  */
-       for (seg = mod->segment; seg; seg = seg->next)
-         if (seg->section == s->sh_info)
-           break;
+       seg = grub_dl_find_segment(mod, s->sh_info);
+        if (!seg)
+         continue;
 
-       if (seg)
-         {
-           if (!mod->symtab)
-             return grub_error (GRUB_ERR_BAD_MODULE, "relocation without 
symbol table");
+       if (!mod->symtab)
+         return grub_error (GRUB_ERR_BAD_MODULE, "relocation without symbol 
table");
 
-           err = grub_arch_dl_relocate_symbols (mod, ehdr, s, seg);
-           if (err)
-             return err;
-         }
+       err = grub_arch_dl_relocate_symbols (mod, ehdr, s, seg);
+       if (err)
+         return err;
       }
 
   return GRUB_ERR_NONE;
 }
 
+/* Only define this on EFI to save space in core */
+#ifdef GRUB_MACHINE_EFI
+static grub_err_t
+grub_dl_set_mem_attrs (grub_dl_t mod, void *ehdr)
+{
+  unsigned i;
+  const Elf_Shdr *s;
+  const Elf_Ehdr *e = ehdr;
+  grub_err_t err;
+#if !defined (__i386__) && !defined (__x86_64__) && !defined(__riscv)
+  grub_size_t arch_addralign = grub_arch_dl_min_alignment ();
+  grub_addr_t tgaddr;
+  grub_size_t tgsz;
+#endif
+
+  for (i = 0, s = (const Elf_Shdr *)((const char *) e + e->e_shoff);
+       i < e->e_shnum;
+       i++, s = (const Elf_Shdr *)((const char *) s + e->e_shentsize))
+    {
+      grub_dl_segment_t seg;
+      grub_uint64_t set_attrs = GRUB_MEM_ATTR_R;
+      grub_uint64_t clear_attrs = GRUB_MEM_ATTR_W|GRUB_MEM_ATTR_X;
+
+      seg = grub_dl_find_segment(mod, i);
+      if (!seg)
+       continue;
+
+      if (seg->size == 0 || !(s->sh_flags & SHF_ALLOC))
+       continue;
+
+      if (s->sh_flags & SHF_WRITE)
+       {
+         set_attrs |= GRUB_MEM_ATTR_W;
+         clear_attrs &= ~GRUB_MEM_ATTR_W;
+       }
+
+      if (s->sh_flags & SHF_EXECINSTR)
+       {
+         set_attrs |= GRUB_MEM_ATTR_X;
+         clear_attrs &= ~GRUB_MEM_ATTR_X;
+       }
+
+      err = grub_update_mem_attrs ((grub_addr_t)(seg->addr), seg->size,
+                                  set_attrs, clear_attrs);
+      if (err != GRUB_ERR_NONE)
+       return err;
+    }
+
+#if !defined (__i386__) && !defined (__x86_64__) && !defined(__riscv)
+  tgaddr = grub_min((grub_addr_t)mod->tramp, (grub_addr_t)mod->got);
+  tgsz = grub_max((grub_addr_t)mod->trampptr, (grub_addr_t)mod->gotptr) - 
tgaddr;
+
+  if (tgsz)
+    {
+      tgsz = ALIGN_UP(tgsz, arch_addralign);
+
+      if (tgaddr < (grub_addr_t)mod->base ||
+          tgsz > (grub_addr_t)-1 - tgaddr ||
+         tgaddr + tgsz > (grub_addr_t)mod->base + mod->sz)
+       return grub_error (GRUB_ERR_BUG,
+                          "BUG: trying to protect pages outside of module "
+                          "allocation (\"%s\"): module base %p, size 0x%"
+                          PRIxGRUB_SIZE "; tramp/GOT base 0x%" PRIxGRUB_ADDR
+                          ", size 0x%" PRIxGRUB_SIZE,
+                          mod->name, mod->base, mod->sz, tgaddr, tgsz);
+      err = grub_update_mem_attrs (tgaddr, tgsz, 
GRUB_MEM_ATTR_R|GRUB_MEM_ATTR_X,
+                                  GRUB_MEM_ATTR_W);
+      if (err != GRUB_ERR_NONE)
+       return err;
+    }
+#endif
+
+  return GRUB_ERR_NONE;
+}
+#endif
+
 /* Load a module from core memory.  */
 grub_dl_t
 grub_dl_load_core_noinit (void *addr, grub_size_t size)
@@ -668,6 +740,7 @@ grub_dl_load_core_noinit (void *addr, grub_size_t size)
   mod->ref_count = 1;
 
   grub_dprintf ("modules", "relocating to %p\n", mod);
+
   /* Me, Vladimir Serbinenko, hereby I add this module check as per new
      GNU module policy. Note that this license check is informative only.
      Modules have to be licensed under GPLv3 or GPLv3+ (optionally
@@ -681,7 +754,12 @@ grub_dl_load_core_noinit (void *addr, grub_size_t size)
       || grub_dl_resolve_dependencies (mod, e)
       || grub_dl_load_segments (mod, e)
       || grub_dl_resolve_symbols (mod, e)
-      || grub_dl_relocate_symbols (mod, e))
+      || grub_dl_relocate_symbols (mod, e)
+#ifdef GRUB_MACHINE_EFI
+      || grub_dl_set_mem_attrs (mod, e))
+#else
+       )
+#endif
     {
       mod->fini = 0;
       grub_dl_unload (mod);
diff --git a/include/grub/dl.h b/include/grub/dl.h
index 8a37cc16f..84a249834 100644
--- a/include/grub/dl.h
+++ b/include/grub/dl.h
@@ -27,6 +27,7 @@
 #include <grub/elf.h>
 #include <grub/list.h>
 #include <grub/misc.h>
+#include <grub/mm.h>
 #endif
 
 /*
@@ -254,6 +255,51 @@ grub_dl_is_persistent (grub_dl_t mod)
   return mod->persistent;
 }
 
+#pragma GCC diagnostic ignored "-Wcast-align"
+
+static inline const char *
+grub_dl_get_section_name (const Elf_Ehdr *e, const Elf_Shdr *s)
+{
+  Elf_Shdr *str_s;
+  const char *str;
+
+  str_s = (Elf_Shdr *) ((char *) e + e->e_shoff + e->e_shstrndx * 
e->e_shentsize);
+  str = (char *) e + str_s->sh_offset;
+
+  return str + s->sh_name;
+}
+
+static inline long
+grub_dl_find_section_index (Elf_Ehdr *e, const char *name)
+{
+  Elf_Shdr *s;
+  const char *str;
+  unsigned i;
+
+  s = (Elf_Shdr *) ((char *) e + e->e_shoff + e->e_shstrndx * e->e_shentsize);
+  str = (char *) e + s->sh_offset;
+
+  for (i = 0, s = (Elf_Shdr *) ((char *) e + e->e_shoff);
+       i < e->e_shnum;
+       i++, s = (Elf_Shdr *) ((char *) s + e->e_shentsize))
+    if (grub_strcmp (str + s->sh_name, name) == 0)
+      return (long)i;
+  return -1;
+}
+
+/* Return the segment for a section of index N */
+static inline grub_dl_segment_t
+grub_dl_find_segment (grub_dl_t mod, unsigned n)
+{
+  grub_dl_segment_t seg;
+
+  for (seg = mod->segment; seg; seg = seg->next)
+    if (seg->section == n)
+      return seg;
+
+  return NULL;
+}
+
 #endif
 
 grub_err_t grub_dl_register_symbol (const char *name, void *addr,
-- 
2.39.2