From: Ariel Marcovitch arielmarcovitch@gmail.com
[ Upstream commit 2225a8dda263edc35a0e8b858fe2945cf6240fde ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/kernel/vmlinux.lds.S | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S index f9081724d6910..a4e576019d79c 100644 --- a/arch/powerpc/kernel/vmlinux.lds.S +++ b/arch/powerpc/kernel/vmlinux.lds.S @@ -210,6 +210,12 @@ 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); @@ -223,6 +229,8 @@ SECTIONS EXIT_TEXT }
+ . = ALIGN(PAGE_SIZE); + INIT_DATA_SECTION(16)
. = ALIGN(8);