ARM: 8722/1: mm: make STRICT_KERNEL_RWX effective for LPAE

philipderrin · Russell King · commit 400eeffaffc7 · 2017-11-21T15:10:07.000Z
Currently, for ARM kernels with CONFIG_ARM_LPAE and CONFIG_STRICT_KERNEL_RWX enabled, the 2MiB pages mapping the kernel code and rodata are writable. They are marked read-only in a software bit (L_PMD_SECT_RDONLY) but the hardware read-only bit is not set (PMD_SECT_AP2). For user mappings, the logic that propagates the software bit to the hardware bit is in set_pmd_at(); but for the kernel, section_update() writes the PMDs directly, skipping this logic. The fix is to set PMD_SECT_AP2 for read-only sections in section_update(), at the same time as L_PMD_SECT_RDONLY. Fixes: 1e34792 ("ARM: 8275/1: mm: fix PMD_SECT_RDONLY undeclared compile error") Signed-off-by: Philip Derrin <philip@cog.systems> Reported-by: Neil Dick <neil@cog.systems> Tested-by: Neil Dick <neil@cog.systems> Tested-by: Laura Abbott <labbott@redhat.com> Reviewed-by: Kees Cook <keescook@chromium.org> Cc: stable@vger.kernel.org Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
@@ -639,8 +639,8 @@ static struct section_perm ro_perms[] = {
 		.start  = (unsigned long)_stext,
 		.end    = (unsigned long)__init_begin,
 #ifdef CONFIG_ARM_LPAE
-		.mask   = ~L_PMD_SECT_RDONLY,
-		.prot   = L_PMD_SECT_RDONLY,
+		.mask   = ~(L_PMD_SECT_RDONLY | PMD_SECT_AP2),
+		.prot   = L_PMD_SECT_RDONLY | PMD_SECT_AP2,
 #else
 		.mask   = ~(PMD_SECT_APX | PMD_SECT_AP_WRITE),
 		.prot   = PMD_SECT_APX | PMD_SECT_AP_WRITE,
