[PATCH v3 48/60] arm64: mm: add LPA2 and 5 level paging support to G-to-nG conversion

Ard Biesheuvel
2023-03-07T14:11:37Z

Add support for 5 level paging in the G-to-nG routine that creates its
own temporary page tables to traverse the swapper page tables. Also add
support for running the 5 level configuration with the top level folded
at runtime, to support CPUs that do not implement the LPA2 extension.

While at it, wire up the level skipping logic so it will also trigger on
4 level configurations with LPA2 enabled at build time but not active at
runtime, as we'll fall back to 3 level paging in that case.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/arm64/kernel/cpufeature.c | 9 ++-
arch/arm64/mm/proc.S | 70 +++++++++++++++++---
2 files changed, 66 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index f8e3f37accdddc86..b0fee11886e54ca2 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1729,6 +1729,9 @@ kpti_install_ng_mappings(const struct arm64_cpu_capabilities *__unused)
pgd_t *kpti_ng_temp_pgd;
u64 alloc = 0;

+ if (levels == 5 && !pgtable_l5_enabled())
+ levels = 4;
+
if (__this_cpu_read(this_cpu_vector) == vectors) {
const char *v = arm64_get_bp_hardening_vector(EL1_VECTOR_KPTI);

@@ -1756,9 +1759,9 @@ kpti_install_ng_mappings(const struct arm64_cpu_capabilities *__unused)
//
// The physical pages are laid out as follows:
//
- // +--------+-/-------+-/------ +-\\--------+
- // : PTE[] : | PMD[] : | PUD[] : || PGD[] :
- // +--------+-\-------+-\------ +-//--------+
+ // +--------+-/-------+-/------ +-/------ +-\\\--------+
+ // : PTE[] : | PMD[] : | PUD[] : | P4D[] : ||| PGD[] :
+ // +--------+-\-------+-\------ +-\------ +-///--------+
// ^
// The first page is mapped into this hierarchy at a PMD_SHIFT
// aligned virtual address, so that we can manipulate the PTE
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 74b846d77b88e843..f425cfc3e4dad188 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -215,16 +215,15 @@ SYM_FUNC_ALIAS(__pi_idmap_cpu_replace_ttbr1, idmap_cpu_replace_ttbr1)
.macro kpti_mk_tbl_ng, type, num_entries
add end_\type\()p, cur_\type\()p, #\num_entries * 8
.Ldo_\type:
- ldr \type, [cur_\type\()p] // Load the entry
+ ldr \type, [cur_\type\()p], #8 // Load the entry and advance
tbz \type, #0, .Lnext_\type // Skip invalid and
tbnz \type, #11, .Lnext_\type // non-global entries
orr \type, \type, #PTE_NG // Same bit for blocks and pages
- str \type, [cur_\type\()p] // Update the entry
+ str \type, [cur_\type\()p, #-8] // Update the entry
.ifnc \type, pte
tbnz \type, #1, .Lderef_\type
.endif
.Lnext_\type:
- add cur_\type\()p, cur_\type\()p, #8
cmp cur_\type\()p, end_\type\()p
b.ne .Ldo_\type
.endm
@@ -234,18 +233,18 @@ SYM_FUNC_ALIAS(__pi_idmap_cpu_replace_ttbr1, idmap_cpu_replace_ttbr1)
* fixmap slot associated with the current level.
*/
.macro kpti_map_pgtbl, type, level
- str xzr, [temp_pte, #8 * (\level + 1)] // break before make
+ str xzr, [temp_pte, #8 * (\level + 2)] // break before make
dsb nshst
- add pte, temp_pte, #PAGE_SIZE * (\level + 1)
+ add pte, temp_pte, #PAGE_SIZE * (\level + 2)
lsr pte, pte, #12
tlbi vaae1, pte
dsb nsh
isb

phys_to_pte pte, cur_\type\()p
- add cur_\type\()p, temp_pte, #PAGE_SIZE * (\level + 1)
+ add cur_\type\()p, temp_pte, #PAGE_SIZE * (\level + 2)
orr pte, pte, pte_flags
- str pte, [temp_pte, #8 * (\level + 1)]
+ str pte, [temp_pte, #8 * (\level + 2)]
dsb nshst
.endm

@@ -278,6 +277,8 @@ SYM_TYPED_FUNC_START(idmap_kpti_install_ng_mappings)
end_ptep .req x15
pte .req x16
valid .req x17
+ cur_p4dp .req x19
+ end_p4dp .req x20

mov x5, x3 // preserve temp_pte arg
mrs swapper_ttb, ttbr1_el1
@@ -285,6 +286,12 @@ SYM_TYPED_FUNC_START(idmap_kpti_install_ng_mappings)

cbnz cpu, __idmap_kpti_secondary

+#if CONFIG_PGTABLE_LEVELS > 4
+ stp x29, x30, [sp, #-32]!
+ mov x29, sp
+ stp x19, x20, [sp, #16]
+#endif
+
/* We're the boot CPU. Wait for the others to catch up */
sevl
1: wfe
@@ -302,9 +309,32 @@ SYM_TYPED_FUNC_START(idmap_kpti_install_ng_mappings)
mov pte_flags, #KPTI_NG_PTE_FLAGS

/* Everybody is enjoying the idmap, so we can rewrite swapper. */
+
+#ifdef CONFIG_ARM64_LPA2
+ /*
+ * If LPA2 support is configured, but 52-bit virtual addressing is not
+ * enabled at runtime, we will fall back to one level of paging less,
+ * and so we have to walk swapper_pg_dir as if we dereferenced its
+ * address from a PGD level entry, and terminate the PGD level loop
+ * right after.
+ */
+ adrp pgd, swapper_pg_dir // walk &swapper_pg_dir at the next level
+ mov cur_pgdp, end_pgdp // must be equal to terminate the PGD loop
+alternative_if_not ARM64_HAS_VA52
+ b .Lderef_pgd // skip to the next level
+alternative_else_nop_endif
+ /*
+ * LPA2 based 52-bit virtual addressing requires 52-bit physical
+ * addressing to be enabled as well. In this case, the shareability
+ * bits are repurposed as physical address bits, and should not be
+ * set in pte_flags.
+ */
+ bic pte_flags, pte_flags, #PTE_SHARED
+#endif
+
/* PGD */
adrp cur_pgdp, swapper_pg_dir
- kpti_map_pgtbl pgd, 0
+ kpti_map_pgtbl pgd, -1
kpti_mk_tbl_ng pgd, PTRS_PER_PGD

/* Ensure all the updated entries are visible to secondary CPUs */
@@ -317,16 +347,33 @@ SYM_TYPED_FUNC_START(idmap_kpti_install_ng_mappings)

/* Set the flag to zero to indicate that we're all done */
str wzr, [flag_ptr]
+#if CONFIG_PGTABLE_LEVELS > 4
+ ldp x19, x20, [sp, #16]
+ ldp x29, x30, [sp], #32
+#endif
ret

.Lderef_pgd:
+ /* P4D */
+ .if CONFIG_PGTABLE_LEVELS > 4
+ p4d .req x30
+ pte_to_phys cur_p4dp, pgd
+ kpti_map_pgtbl p4d, 0
+ kpti_mk_tbl_ng p4d, PTRS_PER_P4D
+ b .Lnext_pgd
+ .else /* CONFIG_PGTABLE_LEVELS <= 4 */
+ p4d .req pgd
+ .set .Lnext_p4d, .Lnext_pgd
+ .endif
+
+.Lderef_p4d:
/* PUD */
.if CONFIG_PGTABLE_LEVELS > 3
pud .req x10
- pte_to_phys cur_pudp, pgd
+ pte_to_phys cur_pudp, p4d
kpti_map_pgtbl pud, 1
kpti_mk_tbl_ng pud, PTRS_PER_PUD
- b .Lnext_pgd
+ b .Lnext_p4d
.else /* CONFIG_PGTABLE_LEVELS <= 3 */
pud .req pgd
.set .Lnext_pud, .Lnext_pgd
@@ -370,6 +417,9 @@ SYM_TYPED_FUNC_START(idmap_kpti_install_ng_mappings)
.unreq end_ptep
.unreq pte
.unreq valid
+ .unreq cur_p4dp
+ .unreq end_p4dp
+ .unreq p4d

/* Secondary CPUs end up here */
__idmap_kpti_secondary:
--
2.39.2