powerpc/mm/radix: Implement STRICT_RWX/mark_rodata_ro() for Radix

The Radix linear mapping code (create_physical_mapping()) tries to use
the largest page size it can at each step. Currently the only reason
it steps down to a smaller page size is if the start addr is
unaligned (never happens in practice), or the end of memory is not
aligned to a huge page boundary.

To support STRICT_RWX we need to break the mapping at __init_begin,
so that the text and rodata prior to that can be marked R_X and the
regular pages after can be marked RW.

Having done that we can now implement mark_rodata_ro() for Radix,
knowing that we won't need to split any mappings.

Signed-off-by: Balbir Singh <bsingharora@gmail.com>
[mpe: Split down to PAGE_SIZE, not 2MB, rewrite change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/mm/pgtable-radix.c b/arch/powerpc/mm/pgtable-radix.c
index 1342859552b1c22046b93f7533835d3c8d46d7e1..8c13e4282308add562bf794be32b989ef90eb803 100644 (file)
--- a/arch/powerpc/mm/pgtable-radix.c
+++ b/arch/powerpc/mm/pgtable-radix.c
@@ -11,6 +11,7 @@
 #include <linux/sched/mm.h>
 #include <linux/memblock.h>
 #include <linux/of_fdt.h>
+#include <linux/mm.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -110,6 +111,49 @@ set_the_pte:
        return 0;
 }
 
+#ifdef CONFIG_STRICT_KERNEL_RWX
+void radix__mark_rodata_ro(void)
+{
+       unsigned long start = (unsigned long)_stext;
+       unsigned long end = (unsigned long)__init_begin;
+       unsigned long idx;
+       pgd_t *pgdp;
+       pud_t *pudp;
+       pmd_t *pmdp;
+       pte_t *ptep;
+
+       start = ALIGN_DOWN(start, PAGE_SIZE);
+       end = PAGE_ALIGN(end); // aligns up
+
+       pr_devel("marking ro start %lx, end %lx\n", start, end);
+
+       for (idx = start; idx < end; idx += PAGE_SIZE) {
+               pgdp = pgd_offset_k(idx);
+               pudp = pud_alloc(&init_mm, pgdp, idx);
+               if (!pudp)
+                       continue;
+               if (pud_huge(*pudp)) {
+                       ptep = (pte_t *)pudp;
+                       goto update_the_pte;
+               }
+               pmdp = pmd_alloc(&init_mm, pudp, idx);
+               if (!pmdp)
+                       continue;
+               if (pmd_huge(*pmdp)) {
+                       ptep = pmdp_ptep(pmdp);
+                       goto update_the_pte;
+               }
+               ptep = pte_alloc_kernel(pmdp, idx);
+               if (!ptep)
+                       continue;
+update_the_pte:
+               radix__pte_update(&init_mm, idx, ptep, _PAGE_WRITE, 0, 0);
+       }
+
+       radix__flush_tlb_kernel_range(start, end);
+}
+#endif /* CONFIG_STRICT_KERNEL_RWX */
+
 static inline void __meminit print_mapping(unsigned long start,
                                           unsigned long end,
                                           unsigned long size)
@@ -125,6 +169,12 @@ static int __meminit create_physical_mapping(unsigned long start,
 {
        unsigned long vaddr, addr, mapping_size = 0;
        pgprot_t prot;
+       unsigned long max_mapping_size;
+#ifdef CONFIG_STRICT_KERNEL_RWX
+       int split_text_mapping = 1;
+#else
+       int split_text_mapping = 0;
+#endif
 
        start = _ALIGN_UP(start, PAGE_SIZE);
        for (addr = start; addr < end; addr += mapping_size) {
@@ -133,9 +183,12 @@ static int __meminit create_physical_mapping(unsigned long start,
 
                gap = end - addr;
                previous_size = mapping_size;
+               max_mapping_size = PUD_SIZE;
 
+retry:
                if (IS_ALIGNED(addr, PUD_SIZE) && gap >= PUD_SIZE &&
-                   mmu_psize_defs[MMU_PAGE_1G].shift)
+                   mmu_psize_defs[MMU_PAGE_1G].shift &&
+                   PUD_SIZE <= max_mapping_size)
                        mapping_size = PUD_SIZE;
                else if (IS_ALIGNED(addr, PMD_SIZE) && gap >= PMD_SIZE &&
                         mmu_psize_defs[MMU_PAGE_2M].shift)
@@ -143,6 +196,18 @@ static int __meminit create_physical_mapping(unsigned long start,
                else
                        mapping_size = PAGE_SIZE;
 
+               if (split_text_mapping && (mapping_size == PUD_SIZE) &&
+                       (addr <= __pa_symbol(__init_begin)) &&
+                       (addr + mapping_size) >= __pa_symbol(_stext)) {
+                       max_mapping_size = PMD_SIZE;
+                       goto retry;
+               }
+
+               if (split_text_mapping && (mapping_size == PMD_SIZE) &&
+                   (addr <= __pa_symbol(__init_begin)) &&
+                   (addr + mapping_size) >= __pa_symbol(_stext))
+                       mapping_size = PAGE_SIZE;
+
                if (mapping_size != previous_size) {
                        print_mapping(start, addr, previous_size);
                        start = addr;

diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c
index fc2e6def2eb7636d45313fe2e6b4a65c3df95e9a..5c0b795d656c4298fc36aaac72d15d58359f23e7 100644 (file)
--- a/arch/powerpc/mm/pgtable_64.c
+++ b/arch/powerpc/mm/pgtable_64.c
@@ -500,7 +500,9 @@ void mark_rodata_ro(void)
                return;
        }
 
-       if (!radix_enabled())
+       if (radix_enabled())
+               radix__mark_rodata_ro();
+       else
                hash__mark_rodata_ro();
 }
 #endif