From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

From: Peter Jones <pjones@redhat.com>

Date: Mon, 21 Mar 2022 17:45:40 -0400

Subject: [PATCH] modules: load module sections at page-aligned addresses

Currently we load module sections at whatever alignment gcc+ld happened

to dump into the ELF section header, which is often pretty useless.  For

example, by default time.mod has these sections on a current x86_64

build:

$ eu-readelf -a grub-core/time.mod |& grep ^Section -A13

Section Headers:

[Nr] Name            Type         Addr  Off      Size     ES Flags Lk Inf Al

[ 0]                 NULL         0     00000000 00000000  0        0   0  0

[ 1] .text           PROGBITS     0     00000040 0000015e  0 AX     0   0  1

[ 2] .rela.text      RELA         0     00000458 000001e0 24 I      8   1  8

[ 3] .rodata.str1.1  PROGBITS     0     0000019e 000000a1  1 AMS    0   0  1

[ 4] .module_license PROGBITS     0     00000240 0000000f  0 A      0   0  8

[ 5] .data           PROGBITS     0     0000024f 00000000  0 WA     0   0  1

[ 6] .bss            NOBITS       0     00000250 00000008  0 WA     0   0  8

[ 7] .modname        PROGBITS     0     00000250 00000005  0        0   0  1

[ 8] .symtab         SYMTAB       0     00000258 00000150 24        9   6  8

[ 9] .strtab         STRTAB       0     000003a8 000000ab  0        0   0  1

[10] .shstrtab       STRTAB       0     00000638 00000059  0        0   0  1

With NX protections being page based, loading sections with either a 1

or 8 *byte* alignment does absolutely nothing to help us out.

This patch switches most EFI platforms to load module sections at 4kB

page-aligned addresses.  To do so, it adds an new per-arch function,

grub_arch_dl_min_alignment(), which returns the alignment needed for

dynamically loaded sections (in bytes).  Currently it sets it to 4096

when GRUB_MACHINE_EFI is true on x86_64, i386, arm, arm64, and emu, and

1-byte alignment on everything else.

It then changes the allocation size computation and the loader code in

grub_dl_load_segments() to align the locations and sizes up to these

boundaries, and fills any added padding with zeros.

All of this happens before relocations are applied, so the relocations

factor that in with no change.

As an aside, initially Daniel Kiper and I thought that it might be a

better idea to split the modules up into top-level sections as

.text.modules, .rodata.modules, .data.modules, etc., so that their page

permissions would get set by the loader that's loading grub itself.

This turns out to have two significant downsides: 1) either in mkimage

or in grub_dl_relocate_symbols(), you wind up having to dynamically

process the relocations to accommodate the moved module sections, and 2)

you then need to change the permissions on the modules and change them

back while relocating them in grub_dl_relocate_symbols(), which means

that any loader that /does/ honor the section flags but does /not/

generally support NX with the memory attributes API will cause grub to

fail.

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

---

 grub-core/kern/arm/dl.c     | 13 +++++++++++++

 grub-core/kern/arm64/dl.c   | 13 +++++++++++++

 grub-core/kern/dl.c         | 29 +++++++++++++++++++++--------

 grub-core/kern/emu/full.c   | 13 +++++++++++++

 grub-core/kern/i386/dl.c    | 13 +++++++++++++

 grub-core/kern/ia64/dl.c    |  9 +++++++++

 grub-core/kern/mips/dl.c    |  8 ++++++++

 grub-core/kern/powerpc/dl.c |  9 +++++++++

 grub-core/kern/riscv/dl.c   | 13 +++++++++++++

 grub-core/kern/sparc64/dl.c |  9 +++++++++

 grub-core/kern/x86_64/dl.c  | 13 +++++++++++++

 include/grub/dl.h           |  2 ++

 docs/grub-dev.texi          |  6 +++---

 13 files changed, 139 insertions(+), 11 deletions(-)

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

index eab9d17ff2..9260737936 100644

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

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

@@ -278,3 +278,16 @@ grub_arch_dl_check_header (void *ehdr)

   return GRUB_ERR_NONE;

 }

+

+/*

+ * Tell the loader what our minimum section alignment is.

+ */

+grub_size_t

+grub_arch_dl_min_alignment (void)

+{

+#ifdef GRUB_MACHINE_EFI

+  return 4096;

+#else

+  return 1;

+#endif

+}

diff --git a/grub-core/kern/arm64/dl.c b/grub-core/kern/arm64/dl.c

index 512e5a80b0..0d4a26857f 100644

--- a/grub-core/kern/arm64/dl.c

+++ b/grub-core/kern/arm64/dl.c

@@ -196,3 +196,16 @@ grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,

   return GRUB_ERR_NONE;

 }

+

+/*

+ * Tell the loader what our minimum section alignment is.

+ */

+grub_size_t

+grub_arch_dl_min_alignment (void)

+{

+#ifdef GRUB_MACHINE_EFI

+  return 4096;

+#else

+  return 1;

+#endif

+}

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

index aef8af8aa7..8c7aacef39 100644

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

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

@@ -277,7 +277,7 @@ grub_dl_load_segments (grub_dl_t mod, const Elf_Ehdr *e)

 {

   unsigned i;

   const Elf_Shdr *s;

-  grub_size_t tsize = 0, talign = 1;

+  grub_size_t tsize = 0, talign = 1, arch_addralign = 1;

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

   grub_size_t tramp;

   grub_size_t got;

@@ -285,16 +285,24 @@ grub_dl_load_segments (grub_dl_t mod, const Elf_Ehdr *e)

 #endif

   char *ptr;

+  arch_addralign = grub_arch_dl_min_alignment ();

+

   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_size_t sh_addralign;

+      grub_size_t sh_size;

+

       if (s->sh_size == 0 || !(s->sh_flags & SHF_ALLOC))

 	continue;

-      tsize = ALIGN_UP (tsize, s->sh_addralign) + s->sh_size;

-      if (talign < s->sh_addralign)

-	talign = s->sh_addralign;

+      sh_addralign = ALIGN_UP(s->sh_addralign, arch_addralign);

+      sh_size = ALIGN_UP(s->sh_size, sh_addralign);

+

+      tsize = ALIGN_UP (tsize, sh_addralign) + sh_size;

+      if (talign < sh_addralign)

+	talign = sh_addralign;

     }

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

@@ -323,6 +331,9 @@ grub_dl_load_segments (grub_dl_t mod, const Elf_Ehdr *e)

        i < e->e_shnum;

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

     {

+      grub_size_t sh_addralign = ALIGN_UP(s->sh_addralign, arch_addralign);

+      grub_size_t sh_size = ALIGN_UP(s->sh_size, sh_addralign);

+

       if (s->sh_flags & SHF_ALLOC)

 	{

 	  grub_dl_segment_t seg;

@@ -335,17 +346,19 @@ grub_dl_load_segments (grub_dl_t mod, const Elf_Ehdr *e)

 	    {

 	      void *addr;

-	      ptr = (char *) ALIGN_UP ((grub_addr_t) ptr, s->sh_addralign);

+	      ptr = (char *) ALIGN_UP ((grub_addr_t) ptr, sh_addralign);

 	      addr = ptr;

-	      ptr += s->sh_size;

+	      ptr += sh_size;

 	      switch (s->sh_type)

 		{

 		case SHT_PROGBITS:

 		  grub_memcpy (addr, (char *) e + s->sh_offset, s->sh_size);

+		  grub_memset ((char *)addr + s->sh_size, 0,

+			       sh_size - s->sh_size);

 		  break;

 		case SHT_NOBITS:

-		  grub_memset (addr, 0, s->sh_size);

+		  grub_memset (addr, 0, sh_size);

 		  break;

 		}

@@ -354,7 +367,7 @@ grub_dl_load_segments (grub_dl_t mod, const Elf_Ehdr *e)

 	  else

 	    seg->addr = 0;

-	  seg->size = s->sh_size;

+	  seg->size = sh_size;

 	  seg->section = i;

 	  seg->next = mod->segment;

 	  mod->segment = seg;

diff --git a/grub-core/kern/emu/full.c b/grub-core/kern/emu/full.c

index e8d63b1f5f..1de1c28eb0 100644

--- a/grub-core/kern/emu/full.c

+++ b/grub-core/kern/emu/full.c

@@ -67,3 +67,16 @@ grub_arch_dl_init_linker (void)

 }

 #endif

+

+/*

+ * Tell the loader what our minimum section alignment is.

+ */

+grub_size_t

+grub_arch_dl_min_alignment (void)

+{

+#ifdef GRUB_MACHINE_EFI

+  return 4096;

+#else

+  return 1;

+#endif

+}

diff --git a/grub-core/kern/i386/dl.c b/grub-core/kern/i386/dl.c

index 1346da5cc9..d6b4681fc9 100644

--- a/grub-core/kern/i386/dl.c

+++ b/grub-core/kern/i386/dl.c

@@ -79,3 +79,16 @@ grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,

   return GRUB_ERR_NONE;

 }

+

+/*

+ * Tell the loader what our minimum section alignment is.

+ */

+grub_size_t

+grub_arch_dl_min_alignment (void)

+{

+#ifdef GRUB_MACHINE_EFI

+  return 4096;

+#else

+  return 1;

+#endif

+}

diff --git a/grub-core/kern/ia64/dl.c b/grub-core/kern/ia64/dl.c

index db59300fea..92d82c5750 100644

--- a/grub-core/kern/ia64/dl.c

+++ b/grub-core/kern/ia64/dl.c

@@ -148,3 +148,12 @@ grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,

     }

   return GRUB_ERR_NONE;

 }

+

+/*

+ * Tell the loader what our minimum section alignment is.

+ */

+grub_size_t

+grub_arch_dl_min_alignment (void)

+{

+  return 1;

+}

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

index 5d7d299c74..6d83bd71e9 100644

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

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

@@ -272,3 +272,11 @@ grub_arch_dl_init_linker (void)

   grub_dl_register_symbol ("_gp_disp", &_gp_disp_dummy, 0, 0);

 }

+/*

+ * Tell the loader what our minimum section alignment is.

+ */

+grub_size_t

+grub_arch_dl_min_alignment (void)

+{

+  return 1;

+}

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

index cdd61b305f..5d9ba2e158 100644

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

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

@@ -167,3 +167,12 @@ grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,

   return GRUB_ERR_NONE;

 }

+

+/*

+ * Tell the loader what our minimum section alignment is.

+ */

+grub_size_t

+grub_arch_dl_min_alignment (void)

+{

+  return 1;

+}

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

index f26b12aaa4..aa18f9e990 100644

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

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

@@ -343,3 +343,16 @@ grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,

   return GRUB_ERR_NONE;

 }

+

+/*

+ * Tell the loader what our minimum section alignment is.

+ */

+grub_size_t

+grub_arch_dl_min_alignment (void)

+{

+#ifdef GRUB_MACHINE_EFI

+  return 4096;

+#else

+  return 1;

+#endif

+}

diff --git a/grub-core/kern/sparc64/dl.c b/grub-core/kern/sparc64/dl.c

index f3d960186b..f054f08241 100644

--- a/grub-core/kern/sparc64/dl.c

+++ b/grub-core/kern/sparc64/dl.c

@@ -189,3 +189,12 @@ grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,

   return GRUB_ERR_NONE;

 }

+

+/*

+ * Tell the loader what our minimum section alignment is.

+ */

+grub_size_t

+grub_arch_dl_min_alignment (void)

+{

+  return 1;

+}

diff --git a/grub-core/kern/x86_64/dl.c b/grub-core/kern/x86_64/dl.c

index e5a8bdcf4f..a105dc50ce 100644

--- a/grub-core/kern/x86_64/dl.c

+++ b/grub-core/kern/x86_64/dl.c

@@ -119,3 +119,16 @@ grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,

   return GRUB_ERR_NONE;

 }

+

+/*

+ * Tell the loader what our minimum section alignment is.

+ */

+grub_size_t

+grub_arch_dl_min_alignment (void)

+{

+#ifdef GRUB_MACHINE_EFI

+  return 4096;

+#else

+  return 1;

+#endif

+}

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

index 618ae6f474..f36ed5cb17 100644

--- a/include/grub/dl.h

+++ b/include/grub/dl.h

@@ -280,6 +280,8 @@ grub_err_t grub_arch_dl_check_header (void *ehdr);

 grub_err_t

 grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,

 			       Elf_Shdr *s, grub_dl_segment_t seg);

+grub_size_t

+grub_arch_dl_min_alignment (void);

 #endif

 #if defined (_mips)

diff --git a/docs/grub-dev.texi b/docs/grub-dev.texi

index 19f708ee66..7b2455a8fe 100644

--- a/docs/grub-dev.texi

+++ b/docs/grub-dev.texi

@@ -755,9 +755,9 @@ declare startup asm file ($cpu_$platform_startup) as well as any other files

 (e.g. init.c and callwrap.S) (e.g. $cpu_$platform = kern/$cpu/$platform/init.c).

 At this stage you will also need to add dummy dl.c and cache.S with functions

 grub_err_t grub_arch_dl_check_header (void *ehdr), grub_err_t

-grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr) (dl.c) and

-void grub_arch_sync_caches (void *address, grub_size_t len) (cache.S). They

-won't be used for now.

+grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr) (dl.c), grub_uint32_t

+grub_arch_dl_min_alignment (void), and void grub_arch_sync_caches (void

+*address, grub_size_t len) (cache.S). They won't be used for now.

 You will need to create directory include/$cpu/$platform and a file

 include/$cpu/types.h. The later folowing this template: