arm64: Extend early page table code to allow for larger kernels

Currently the early assembler page table code assumes that precisely
1xpgd, 1xpud, 1xpmd are sufficient to represent the early kernel text
mappings.

Unfortunately this is rarely the case when running with a 16KB granule,
and we also run into limits with 4KB granule when building much larger
kernels.

This patch re-writes the early page table logic to compute indices of
mappings for each level of page table, and if multiple indices are
required, the next-level page table is scaled up accordingly.

Also the required size of the swapper_pg_dir is computed at link time
to cover the mapping [KIMAGE_ADDR + VOFFSET, _end]. When KASLR is
enabled, an extra page is set aside for each level that may require extra
entries at runtime.

Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

2 files changed, 47 insertions, 1 deletions

diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
index 77a27af01371..82386e860dd2 100644
--- a/arch/arm64/include/asm/kernel-pgtable.h
+++ b/arch/arm64/include/asm/kernel-pgtable.h
@@ -52,7 +52,52 @@
 #define IDMAP_PGTABLE_LEVELS	(ARM64_HW_PGTABLE_LEVELS(PHYS_MASK_SHIFT))
 #endif
 
-#define SWAPPER_DIR_SIZE	(SWAPPER_PGTABLE_LEVELS * PAGE_SIZE)
+
+/*
+ * If KASLR is enabled, then an offset K is added to the kernel address
+ * space. The bottom 21 bits of this offset are zero to guarantee 2MB
+ * alignment for PA and VA.
+ *
+ * For each pagetable level of the swapper, we know that the shift will
+ * be larger than 21 (for the 4KB granule case we use section maps thus
+ * the smallest shift is actually 30) thus there is the possibility that
+ * KASLR can increase the number of pagetable entries by 1, so we make
+ * room for this extra entry.
+ *
+ * Note KASLR cannot increase the number of required entries for a level
+ * by more than one because it increments both the virtual start and end
+ * addresses equally (the extra entry comes from the case where the end
+ * address is just pushed over a boundary and the start address isn't).
+ */
+
+#ifdef CONFIG_RANDOMIZE_BASE
+#define EARLY_KASLR	(1)
+#else
+#define EARLY_KASLR	(0)
+#endif
+
+#define EARLY_ENTRIES(vstart, vend, shift) (((vend) >> (shift)) \
+					- ((vstart) >> (shift)) + 1 + EARLY_KASLR)
+
+#define EARLY_PGDS(vstart, vend) (EARLY_ENTRIES(vstart, vend, PGDIR_SHIFT))
+
+#if SWAPPER_PGTABLE_LEVELS > 3
+#define EARLY_PUDS(vstart, vend) (EARLY_ENTRIES(vstart, vend, PUD_SHIFT))
+#else
+#define EARLY_PUDS(vstart, vend) (0)
+#endif
+
+#if SWAPPER_PGTABLE_LEVELS > 2
+#define EARLY_PMDS(vstart, vend) (EARLY_ENTRIES(vstart, vend, SWAPPER_TABLE_SHIFT))
+#else
+#define EARLY_PMDS(vstart, vend) (0)
+#endif
+
+#define EARLY_PAGES(vstart, vend) ( 1 			/* PGDIR page */				\
+			+ EARLY_PGDS((vstart), (vend)) 	/* each PGDIR needs a next level page table */	\
+			+ EARLY_PUDS((vstart), (vend))	/* each PUD needs a next level page table */	\
+			+ EARLY_PMDS((vstart), (vend)))	/* each PMD needs a next level page table */
+#define SWAPPER_DIR_SIZE (PAGE_SIZE * EARLY_PAGES(KIMAGE_VADDR + TEXT_OFFSET, _end))
 #define IDMAP_DIR_SIZE		(IDMAP_PGTABLE_LEVELS * PAGE_SIZE)
 
 #ifdef CONFIG_ARM64_SW_TTBR0_PAN
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index bfa237e892f1..54b0a8398055 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -706,6 +706,7 @@ static inline void pmdp_set_wrprotect(struct mm_struct *mm,
 #endif
 
 extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
+extern pgd_t swapper_pg_end[];
 extern pgd_t idmap_pg_dir[PTRS_PER_PGD];
 extern pgd_t tramp_pg_dir[PTRS_PER_PGD];