| From 13b0566962914e167cb3238fbe29ced618f07a27 Mon Sep 17 00:00:00 2001 |
| From: Will Deacon <will@kernel.org> |
| Date: Thu, 22 Sep 2022 22:57:15 +0100 |
| Subject: vmlinux.lds.h: CFI: Reduce alignment of jump-table to function alignment |
| |
| From: Will Deacon <will@kernel.org> |
| |
| commit 13b0566962914e167cb3238fbe29ced618f07a27 upstream. |
| |
| Due to undocumented, hysterical raisins on x86, the CFI jump-table |
| sections in .text are needlessly aligned to PMD_SIZE in the vmlinux |
| linker script. When compiling a CFI-enabled arm64 kernel with a 64KiB |
| page-size, a PMD maps 512MiB of virtual memory and so the .text section |
| increases to a whopping 940MiB and blows the final Image up to 960MiB. |
| Others report a link failure. |
| |
| Since the CFI jump-table requires only instruction alignment, reduce the |
| alignment directives to function alignment for parity with other parts |
| of the .text section. This reduces the size of the .text section for the |
| aforementioned 64KiB page size arm64 kernel to 19MiB for a much more |
| reasonable total Image size of 39MiB. |
| |
| Cc: Sami Tolvanen <samitolvanen@google.com> |
| Cc: Mark Rutland <mark.rutland@arm.com> |
| Cc: "Mohan Rao .vanimina" <mailtoc.mohanrao@gmail.com> |
| Cc: Kees Cook <keescook@chromium.org> |
| Cc: Nathan Chancellor <nathan@kernel.org> |
| Cc: <stable@vger.kernel.org> |
| Link: https://lore.kernel.org/all/CAL_GTzigiNOMYkOPX1KDnagPhJtFNqSK=1USNbS0wUL4PW6-Uw@mail.gmail.com/ |
| Fixes: cf68fffb66d6 ("add support for Clang CFI") |
| Reviewed-by: Mark Rutland <mark.rutland@arm.com> |
| Tested-by: Mark Rutland <mark.rutland@arm.com> |
| Reviewed-by: Sami Tolvanen <samitolvanen@google.com> |
| Reviewed-by: Kees Cook <keescook@chromium.org> |
| Link: https://lore.kernel.org/r/20220922215715.13345-1-will@kernel.org |
| Signed-off-by: Will Deacon <will@kernel.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| include/asm-generic/vmlinux.lds.h | 3 +-- |
| 1 file changed, 1 insertion(+), 2 deletions(-) |
| |
| --- a/include/asm-generic/vmlinux.lds.h |
| +++ b/include/asm-generic/vmlinux.lds.h |
| @@ -549,10 +549,9 @@ |
| */ |
| #ifdef CONFIG_CFI_CLANG |
| #define TEXT_CFI_JT \ |
| - . = ALIGN(PMD_SIZE); \ |
| + ALIGN_FUNCTION(); \ |
| __cfi_jt_start = .; \ |
| *(.text..L.cfi.jumptable .text..L.cfi.jumptable.*) \ |
| - . = ALIGN(PMD_SIZE); \ |
| __cfi_jt_end = .; |
| #else |
| #define TEXT_CFI_JT |
