On 29/05/2026 13:19, Ard Biesheuvel wrote: > On Fri, 29 May 2026, at 10:27, Kevin Brodsky wrote: >> On 26/05/2026 19:58, Ard Biesheuvel wrote: >>> From: Ard Biesheuvel <[email protected]> >>> >>> Move the fixmap and kasan page tables out of the BSS section, and place >>> them at the end of the image, right before the init_pg_dir section where >>> some of the other statically allocated page tables live. >>> >>> These page tables are currently the only data objects in vmlinux that >>> are meant to be accessed via the kernel image's linear alias, and so >>> placing them together allows the remainder of the data/bss section to be >>> remapped read-only or unmapped entirely. >>> >>> Reviewed-by: Kevin Brodsky <[email protected]> >>> Signed-off-by: Ard Biesheuvel <[email protected]> >>> --- >>> arch/arm64/include/asm/mmu.h | 2 ++ >>> arch/arm64/kernel/vmlinux.lds.S | 8 +++++++- >>> arch/arm64/mm/fixmap.c | 6 +++--- >>> arch/arm64/mm/kasan_init.c | 2 +- >>> 4 files changed, 13 insertions(+), 5 deletions(-) >>> >>> diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h >>> index 5e1211c540ab..fb95754f2876 100644 >>> --- a/arch/arm64/include/asm/mmu.h >>> +++ b/arch/arm64/include/asm/mmu.h >>> @@ -13,6 +13,8 @@ >>> >>> #ifndef __ASSEMBLER__ >>> >>> +#define __pgtbl_bss __section(".pgdir.bss") __aligned(PAGE_SIZE) >>> + >>> #include <linux/refcount.h> >>> #include <asm/cpufeature.h> >>> >>> diff --git a/arch/arm64/kernel/vmlinux.lds.S >>> b/arch/arm64/kernel/vmlinux.lds.S >>> index e1ac876200a3..2b0ebfb30c63 100644 >>> --- a/arch/arm64/kernel/vmlinux.lds.S >>> +++ b/arch/arm64/kernel/vmlinux.lds.S >>> @@ -349,9 +349,15 @@ SECTIONS >>> _edata = .; >>> >>> /* start of zero-init region */ >>> - BSS_SECTION(SBSS_ALIGN, 0, 0) >>> + BSS_SECTION(SBSS_ALIGN, 0, PAGE_SIZE) >>> __pi___bss_start = __bss_start; >>> >>> + /* fixmap BSS starts here - preceding data/BSS is omitted from the >>> linear map */ >>> + .pgdir.bss (NOLOAD) : ALIGN(PAGE_SIZE) { >> Do we actually need the NOLOAD type here? > Yes, otherwise it is emitted as PROGBITS, resulting in all of BSS to be > emitted into Image.
That's rather strange, aren't the .pgdir.bss input sections already NOBITS since __pgtbl_bss is only used on default-initialised globals? Also AFAIU NOLOAD does not prevent the output section from being emitted into the ELF file. - Kevin
