From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

From: Peter Jones <pjones@redhat.com>

Date: Mon, 21 Mar 2022 17:46:35 -0400

Subject: [PATCH] nx: set page permissions for loaded modules.

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.

Signed-off-by: Peter Jones <pjones@redhat.com>

[rharwood: arm tgptr -> tgaddr]

Signed-off-by: Robbie Harwood <rharwood@redhat.com>

---

 grub-core/kern/dl.c | 120 +++++++++++++++++++++++++++++++++++++++-------------

 include/grub/dl.h   |  44 +++++++++++++++++++

 2 files changed, 134 insertions(+), 30 deletions(-)

diff --git a/grub-core/kern/dl.c b/grub-core/kern/dl.c

index 8c7aacef39..d5de80186f 100644

--- a/grub-core/kern/dl.c

+++ b/grub-core/kern/dl.c

@@ -285,6 +285,8 @@ grub_dl_load_segments (grub_dl_t mod, const Elf_Ehdr *e)

 #endif

   char *ptr;

+  grub_dprintf ("modules", "loading segments for \"%s\"\n", mod->name);

+

   arch_addralign = grub_arch_dl_min_alignment ();

   for (i = 0, s = (const Elf_Shdr *)((const char *) e + e->e_shoff);

@@ -384,6 +386,7 @@ grub_dl_load_segments (grub_dl_t mod, const Elf_Ehdr *e)

   ptr += got;

 #endif

+  grub_dprintf ("modules", "done loading segments for \"%s\"\n", mod->name);

   return GRUB_ERR_NONE;

 }

@@ -517,23 +520,6 @@ grub_dl_find_section (Elf_Ehdr *e, const char *name)

       return s;

   return NULL;

 }

-static 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;

-}

 /* Me, Vladimir Serbinenko, hereby I add this module check as per new

    GNU module policy. Note that this license check is informative only.

@@ -662,6 +648,7 @@ grub_dl_relocate_symbols (grub_dl_t mod, void *ehdr)

   Elf_Shdr *s;

   unsigned i;

+  grub_dprintf ("modules", "relocating symbols for \"%s\"\n", mod->name);

   for (i = 0, s = (Elf_Shdr *) ((char *) e + e->e_shoff);

        i < e->e_shnum;

        i++, s = (Elf_Shdr *) ((char *) s + e->e_shentsize))

@@ -670,24 +657,95 @@ 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;

       }

+  grub_dprintf ("modules", "done relocating symbols for \"%s\"\n", mod->name);

   return GRUB_ERR_NONE;

 }

+

+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;

+#if !defined (__i386__) && !defined (__x86_64__) && !defined(__riscv)

+  grub_size_t arch_addralign = grub_arch_dl_min_alignment ();

+  grub_addr_t tgaddr;

+  grub_uint64_t tgsz;

+#endif

+

+  grub_dprintf ("modules", "updating memory attributes for \"%s\"\n",

+		mod->name);

+  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;

+	}

+

+      grub_dprintf ("modules", "setting memory attrs for section \"%s\" to -%s%s%s+%s%s%s\n",

+		    grub_dl_get_section_name(e, s),

+		    (clear_attrs & GRUB_MEM_ATTR_R) ? "r" : "",

+		    (clear_attrs & GRUB_MEM_ATTR_W) ? "w" : "",

+		    (clear_attrs & GRUB_MEM_ATTR_X) ? "x" : "",

+		    (set_attrs & GRUB_MEM_ATTR_R) ? "r" : "",

+		    (set_attrs & GRUB_MEM_ATTR_W) ? "w" : "",

+		    (set_attrs & GRUB_MEM_ATTR_X) ? "x" : "");

+      grub_update_mem_attrs ((grub_addr_t)(seg->addr), seg->size, set_attrs, clear_attrs);

+    }

+

+#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);

+

+      grub_dprintf ("modules", "updating attributes for GOT and trampolines\n",

+		    mod->name);

+      grub_update_mem_attrs (tgaddr, tgsz, GRUB_MEM_ATTR_R|GRUB_MEM_ATTR_X,

+			     GRUB_MEM_ATTR_W);

+    }

+#endif

+

+  grub_dprintf ("modules", "done updating module memory attributes for \"%s\"\n",

+		mod->name);

+

+  return GRUB_ERR_NONE;

+}

+

 static void

 grub_dl_print_gdb_info (grub_dl_t mod, Elf_Ehdr *e)

 {

@@ -753,6 +811,7 @@ 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

@@ -766,7 +825,8 @@ 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)

+      || grub_dl_set_mem_attrs (mod, e))

     {

       mod->fini = 0;

       grub_dl_unload (mod);

diff --git a/include/grub/dl.h b/include/grub/dl.h

index f36ed5cb17..45ac8e339f 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

 /*

@@ -268,6 +269,49 @@ grub_dl_is_persistent (grub_dl_t mod)

   return mod->persistent;

 }

+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

 void * EXPORT_FUNC(grub_resolve_symbol) (const char *name);