[PATCH 5.10 089/199] powerpc: Fix alignment bug within the init sections

Greg Kroah-Hartman
2021-01-26T09:42:12Z

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 50507dac118ae..83281aee14d2f 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);
--
2.27.0