grub2/0171-modules-load-module-sections-at-page-aligned-address.patch

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 eab9d17ff2d..92607379366 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 a2b5789a9dd..95c6d5bf4e5 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 832c6188df4..775b367287e 100644
--- a/grub-core/kern/dl.c
+++ b/grub-core/kern/dl.c
@@ -268,7 +268,7 @@ 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) && \
   !defined (__loongarch__)
   grub_size_t tramp;
@@ -277,16 +277,24 @@ 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) && \
@@ -316,6 +324,9 @@ 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;
@@ -328,17 +339,19 @@ 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;
 		}
 
@@ -347,7 +360,7 @@ 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 e8d63b1f5f9..1de1c28eb09 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 1346da5cc91..d6b4681fc93 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 db59300fea3..92d82c57505 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 5b02f97fca7..db411899dbe 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 7b6418eabd7..0eb8bc5bd31 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 896653bb41c..1fa085b4acf 100644
--- a/grub-core/kern/riscv/dl.c
+++ b/grub-core/kern/riscv/dl.c
@@ -344,3 +344,16 @@ 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 f3d960186ba..f054f08241d 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 e5a8bdcf4f9..a105dc50cea 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 216f8b903ac..9f86765c8e9 100644
--- a/include/grub/dl.h
+++ b/include/grub/dl.h
@@ -279,6 +279,8 @@ 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 04c6678cb6b..8ad5494f5ce 100644
--- a/docs/grub-dev.texi
+++ b/docs/grub-dev.texi
@@ -996,9 +996,9 @@ 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 latter following this template: