The following commit has been merged into the objtool/urgent branch of tip:
Commit-ID: 68f3ea7ee199ef77551e090dfef5a49046ea8443 Gitweb: https://git.kernel.org/tip/68f3ea7ee199ef77551e090dfef5a49046ea8443 Author: Ard Biesheuvel ardb@kernel.org AuthorDate: Fri, 21 Feb 2025 14:57:06 +01:00 Committer: Josh Poimboeuf jpoimboe@kernel.org CommitterDate: Tue, 25 Feb 2025 09:46:15 -08:00
vmlinux.lds: Ensure that const vars with relocations are mapped R/O
In the kernel, there are architectures (x86, arm64) that perform boot-time relocation (for KASLR) without relying on PIE codegen. In this case, all const global objects are emitted into .rodata, including const objects with fields that will be fixed up by the boot-time relocation code. This implies that .rodata (and .text in some cases) need to be writable at boot, but they will usually be mapped read-only as soon as the boot completes.
When using PIE codegen, the compiler will emit const global objects into .data.rel.ro rather than .rodata if the object contains fields that need such fixups at boot-time. This permits the linker to annotate such regions as requiring read-write access only at load time, but not at execution time (in user space), while keeping .rodata truly const (in user space, this is important for reducing the CoW footprint of dynamic executables).
This distinction does not matter for the kernel, but it does imply that const data will end up in writable memory if the .data.rel.ro sections are not treated in a special way, as they will end up in the writable .data segment by default.
So emit .data.rel.ro into the .rodata segment.
Cc: stable@vger.kernel.org Signed-off-by: Ard Biesheuvel ardb@kernel.org Link: https://lore.kernel.org/r/20250221135704.431269-5-ardb+git@google.com Signed-off-by: Josh Poimboeuf jpoimboe@kernel.org --- include/asm-generic/vmlinux.lds.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 5450401..337d333 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -457,7 +457,7 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG) . = ALIGN((align)); \ .rodata : AT(ADDR(.rodata) - LOAD_OFFSET) { \ __start_rodata = .; \ - *(.rodata) *(.rodata.*) \ + *(.rodata) *(.rodata.*) *(.data.rel.ro*) \ SCHED_DATA \ RO_AFTER_INIT_DATA /* Read only after init */ \ . = ALIGN(8); \