Re: [PATCH v5 32/36] x86/boot/compressed: Reorganize zero-size section asserts
From: Arvind Sankar <hidden>
Date: 2020-08-01 01:48:01
Also in:
linux-arch, linux-efi, lkml
On Fri, Jul 31, 2020 at 04:08:16PM -0700, Kees Cook wrote:
quoted hunk ↗ jump to hunk
For readability, move the zero-sized sections to the end after DISCARDS and mark them NOLOAD for good measure. Signed-off-by: Kees Cook <redacted> --- arch/x86/boot/compressed/vmlinux.lds.S | 42 +++++++++++++++----------- 1 file changed, 25 insertions(+), 17 deletions(-)diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S index 3c2ee9a5bf43..42dea70a5091 100644 --- a/arch/x86/boot/compressed/vmlinux.lds.S +++ b/arch/x86/boot/compressed/vmlinux.lds.S@@ -42,18 +42,16 @@ SECTIONS *(.rodata.*) _erodata = . ; } - .rel.dyn : { - *(.rel.*) - } - .rela.dyn : { - *(.rela.*) - } - .got : { - *(.got) - } .got.plt : { *(.got.plt) } + ASSERT(SIZEOF(.got.plt) == 0 || +#ifdef CONFIG_X86_64 + SIZEOF(.got.plt) == 0x18, +#else + SIZEOF(.got.plt) == 0xc, +#endif + "Unexpected GOT/PLT entries detected!") .data : { _data = . ;@@ -85,13 +83,23 @@ SECTIONS ELF_DETAILS DISCARDS -} -ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!") -#ifdef CONFIG_X86_64 -ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, "Unexpected GOT/PLT entries detected!") -#else -ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0xc, "Unexpected GOT/PLT entries detected!") -#endif + /* + * Sections that should stay zero sized, which is safer to + * explicitly check instead of blindly discarding. + */ + .got (NOLOAD) : { + *(.got) + } + ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!") -ASSERT(SIZEOF(.rel.dyn) == 0 && SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations detected!") + /* ld.lld does not like .rel* sections being made "NOLOAD". */ + .rel.dyn : { + *(.rel.*) + } + ASSERT(SIZEOF(.rel.dyn) == 0, "Unexpected run-time relocations (.rel) detected!") + .rela.dyn : { + *(.rela.*) + } + ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!") +}-- 2.25.1
There's no point in marking zero-size sections NOLOAD -- if the ASSERT's passed, they won't be present in the file at all anyway. The only section for which there might be a point is .got.plt, which is non-empty on 32-bit, and only if it is first moved to the end. That saves a few bytes. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel