The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2225a8dda263edc35a0e8b858fe2945cf6240fde Mon Sep 17 00:00:00 2001

From: Ariel Marcovitch arielmarcovitch@gmail.com Date: Sat, 2 Jan 2021 22:11:56 +0200 Subject: [PATCH] powerpc: Fix alignment bug within the init sections

This is a bug that causes early crashes in builds with an .exit.text section smaller than a page and an .init.text section that ends in the beginning of a physical page (this is kinda random, which might explain why this wasn't really encountered before).

The init sections are ordered like this: .init.text .exit.text .init.data

Currently, these sections aren't page aligned.

Because the init code might become read-only at runtime and because the .init.text section can potentially reside on the same physical page as .init.data, the beginning of .init.data might be mapped read-only along with .init.text.

Then when the kernel tries to modify a variable in .init.data (like kthreadd_done, used in kernel_init()) the kernel panics.

To avoid this, make _einittext page aligned and also align .exit.text to make sure .init.data is always seperated from the text segments.

Fixes: 060ef9d89d18 ("powerpc32: PAGE_EXEC required for inittext") Signed-off-by: Ariel Marcovitch ariel.marcovitch@gmail.com Reviewed-by: Christophe Leroy christophe.leroy@csgroup.eu Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20210102201156.10805-1-ariel.marcovitch@gmail.com

diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S index 8e0b1298bf19..4ab426b8b0e0 100644 --- a/arch/powerpc/kernel/vmlinux.lds.S +++ b/arch/powerpc/kernel/vmlinux.lds.S @@ -187,6 +187,12 @@ SECTIONS .init.text : AT(ADDR(.init.text) - LOAD_OFFSET) { _sinittext = .; INIT_TEXT + + /* + *.init.text might be RO so we must ensure this section ends on + * a page boundary. + */ + . = ALIGN(PAGE_SIZE); _einittext = .; #ifdef CONFIG_PPC64 *(.tramp.ftrace.init); @@ -200,6 +206,8 @@ SECTIONS EXIT_TEXT }

+ . = ALIGN(PAGE_SIZE); + INIT_DATA_SECTION(16)

. = ALIGN(8);