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

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

[Russell Currey]

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

[PATCH 2/2] powerpc: Remove STRICT_KERNEL_RWX incompatibility with RELOCATABLE

[Russell Currey]

I have tested this with the Radix MMU and everything seems to work, and
the previous patch for Hash seems to fix everything too.
STRICT_KERNEL_RWX should still be disabled by default for now.

Please test STRICT_KERNEL_RWX + RELOCATABLE!

Signed-off-by: Russell Currey <ruscur@russell.cc>
---
 arch/powerpc/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 1ec34e16ed65..6093c48976bf 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -133,7 +133,7 @@ config PPC
 	select ARCH_HAS_PTE_SPECIAL
 	select ARCH_HAS_MEMBARRIER_CALLBACKS
 	select ARCH_HAS_SCALED_CPUTIME		if VIRT_CPU_ACCOUNTING_NATIVE && PPC_BOOK3S_64
-	select ARCH_HAS_STRICT_KERNEL_RWX	if ((PPC_BOOK3S_64 || PPC32) && !RELOCATABLE && !HIBERNATION)
+	select ARCH_HAS_STRICT_KERNEL_RWX	if ((PPC_BOOK3S_64 || PPC32) && !HIBERNATION)
 	select ARCH_HAS_TICK_BROADCAST		if GENERIC_CLOCKEVENTS_BROADCAST
 	select ARCH_HAS_UACCESS_FLUSHCACHE
 	select ARCH_HAS_UACCESS_MCSAFE		if PPC64
-- 
2.24.1

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

[Michael Ellerman]

On Tue, 2019-12-24 at 06:41:25 UTC, Russell Currey wrote:
> 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>

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/970d54f99ceac5bbf27929cb5ebfe18338ba1543

cheers