[PATCH 05/15] modules: load module sections at page-aligned addresses

From: Mate Kukri <mate.kukri@canonical.com>
To: grub-devel@gnu.org
Cc: Peter Jones <pjones@redhat.com>,
	Jan Setje-Eilers <jan.setjeeilers@oracle.com>,
	Mate Kukri <mate.kukri@canonical.com>
Subject: [PATCH 05/15] modules: load module sections at page-aligned addresses
Date: Fri, 24 May 2024 12:03:52 +0100	[thread overview]
Message-ID: <20240524110402.203880-6-mate.kukri@canonical.com> (raw)
In-Reply-To: <20240524110402.203880-1-mate.kukri@canonical.com>

From: Peter Jones <pjones@redhat.com>

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>
(cherry picked from commit 887f1d8fa976bb7ac4e283e896c3be9d70f8b150)
Signed-off-by: Jan Setje-Eilers <jan.setjeeilers@oracle.com>

 Conflicts:
	grub-core/kern/dl.c	(obvious)

Signed-off-by: Mate Kukri <mate.kukri@canonical.com>
---
 docs/grub-dev.texi          |  6 +++---
 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 ++
 13 files changed, 139 insertions(+), 11 deletions(-)

diff --git a/docs/grub-dev.texi b/docs/grub-dev.texi
index 1276c5930..2f782cda5 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:
diff --git a/grub-core/kern/arm/dl.c b/grub-core/kern/arm/dl.c
index eab9d17ff..926073793 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 a2b5789a9..95c6d5bf4 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 37db9fab0..fb06fd8c6 100644
--- a/grub-core/kern/dl.c
+++ b/grub-core/kern/dl.c
@@ -224,7 +224,7 @@ 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;
@@ -233,16 +233,24 @@ 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) && \
@@ -272,6 +280,9 @@ 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;
@@ -284,17 +295,19 @@ 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;
 		}
 
@@ -303,7 +316,7 @@ 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 e8d63b1f5..1de1c28eb 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 1346da5cc..d6b4681fc 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 db59300fe..92d82c575 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 5b02f97fc..db411899d 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 7b6418eab..0eb8bc5bd 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 896653bb4..1fa085b4a 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 f3d960186..f054f0824 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 e5a8bdcf4..a105dc50c 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 750fc8d3d..8a37cc16f 100644
--- a/include/grub/dl.h
+++ b/include/grub/dl.h
@@ -264,6 +264,8 @@ 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)
-- 
2.39.2


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