arm64: lds: move .got section out of .text

Currently, the .got section is placed within the output section .text.
However, when .got is non-empty, the SHF_WRITE flag is set for .text
when linked by lld. GNU ld recognizes .text as a special section and
ignores the SHF_WRITE flag. By renaming .text, we can also get the
SHF_WRITE flag.

The kernel has performed R_AARCH64_RELATIVE resolving very early, and can
then assume that .got is read-only. Let's move .got to the vmlinux_rodata
pseudo-segment.

As Ard Biesheuvel notes:

"This matters to consumers of the vmlinux ELF representation of the
kernel image, such as syzkaller, which disregards writable PT_LOAD
segments when resolving code symbols. The kernel itself does not care
about this distinction, but given that the GOT contains data and not
code, it does not require executable permissions, and therefore does
not belong in .text to begin with."

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Fangrui Song <maskray@google.com>
Link: https://lore.kernel.org/r/20230502074105.1541926-1-maskray@google.com
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index b9202c2..3cd7e76 100644 (file)
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -181,18 +181,8 @@ SECTIONS
                        KPROBES_TEXT
                        HYPERVISOR_TEXT
                        *(.gnu.warning)
-               . = ALIGN(16);
-               *(.got)                 /* Global offset table          */
        }
 
-       /*
-        * Make sure that the .got.plt is either completely empty or it
-        * contains only the lazy dispatch entries.
-        */
-       .got.plt : { *(.got.plt) }
-       ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18,
-              "Unexpected GOT/PLT entries detected!")
-
        . = ALIGN(SEGMENT_ALIGN);
        _etext = .;                     /* End of text section */
 
@@ -201,6 +191,15 @@ SECTIONS
 
        HYPERVISOR_DATA_SECTIONS
 
+       .got : { *(.got) }
+       /*
+        * Make sure that the .got.plt is either completely empty or it
+        * contains only the lazy dispatch entries.
+        */
+       .got.plt : { *(.got.plt) }
+       ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18,
+              "Unexpected GOT/PLT entries detected!")
+
        /* code sections that are never executed via the kernel mapping */
        .rodata.text : {
                TRAMP_TEXT