[PATCH 1/2] powerpc/book3s64/hash: Disable 16M linear mapping size if not aligned

Russell Currey
2019-12-24T06:42:04Z

With STRICT_KERNEL_RWX on in a relocatable kernel under the hash MMU, if
the position the kernel is loaded at is not 16M aligned, the kernel
miscalculates its ALIGN*()s and things go horribly wrong.

We can easily avoid this when selecting the linear mapping size, so do
so and print a warning. I tested this for various alignments and as
long as the position is 64K aligned it's fine (the base requirement for
powerpc).

Signed-off-by: Russell Currey <ruscur@russell.cc>
---
arch/powerpc/mm/book3s64/hash_utils.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
index b30435c7d804..523d4d39d11e 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -652,6 +652,7 @@ static void init_hpte_page_sizes(void)

static void __init htab_init_page_sizes(void)
{
+ bool aligned = true;
init_hpte_page_sizes();

if (!debug_pagealloc_enabled()) {
@@ -659,7 +660,15 @@ static void __init htab_init_page_sizes(void)
* Pick a size for the linear mapping. Currently, we only
* support 16M, 1M and 4K which is the default
*/
- if (mmu_psize_defs[MMU_PAGE_16M].shift)
+ if (IS_ENABLED(STRICT_KERNEL_RWX) &&
+ (unsigned long)_stext % 0x1000000) {
+ if (mmu_psize_defs[MMU_PAGE_16M].shift)
+ pr_warn("Kernel not 16M aligned, "
+ "disabling 16M linear map alignment");
+ aligned = false;
+ }
+
+ if (mmu_psize_defs[MMU_PAGE_16M].shift && aligned)
mmu_linear_psize = MMU_PAGE_16M;
else if (mmu_psize_defs[MMU_PAGE_1M].shift)
mmu_linear_psize = MMU_PAGE_1M;
--
2.24.1