Merge branch 'for-next/kpti' into for-next/core

* for-next/kpti:
  arm64: correct the effect of mitigations off on kpti
  arm64: entry: simplify trampoline data page
  arm64: mm: install KPTI nG mappings with MMU enabled
  arm64: kpti-ng: simplify page table traversal logic

Documentation/admin-guide/kernel-parameters.txt

@@ -3161,7 +3161,7 @@
 				improves system performance, but it may also
 				expose users to several CPU vulnerabilities.
 				Equivalent to: nopti [X86,PPC]
-					       kpti=0 [ARM64]
+					       if nokaslr then kpti=0 [ARM64]
 					       nospectre_v1 [X86,PPC]
 					       nobp=0 [S390]
 					       nospectre_v2 [X86,PPC,S390,ARM64]

arch/arm64/include/asm/fixmap.h

@@ -62,10 +62,12 @@ enum fixed_addresses {
 #endif /* CONFIG_ACPI_APEI_GHES */
 
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+#ifdef CONFIG_RELOCATABLE
+	FIX_ENTRY_TRAMP_TEXT4,	/* one extra slot for the data page */
+#endif
 	FIX_ENTRY_TRAMP_TEXT3,
 	FIX_ENTRY_TRAMP_TEXT2,
 	FIX_ENTRY_TRAMP_TEXT1,
-	FIX_ENTRY_TRAMP_DATA,
 #define TRAMP_VALIAS		(__fix_to_virt(FIX_ENTRY_TRAMP_TEXT1))
 #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
 	__end_of_permanent_fixed_addresses,

arch/arm64/kernel/cpufeature.c

@@ -1646,14 +1646,34 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
 }
 
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+#define KPTI_NG_TEMP_VA		(-(1UL << PMD_SHIFT))
+
+extern
+void create_kpti_ng_temp_pgd(pgd_t *pgdir, phys_addr_t phys, unsigned long virt,
+			     phys_addr_t size, pgprot_t prot,
+			     phys_addr_t (*pgtable_alloc)(int), int flags);
+
+static phys_addr_t kpti_ng_temp_alloc;
+
+static phys_addr_t kpti_ng_pgd_alloc(int shift)
+{
+	kpti_ng_temp_alloc -= PAGE_SIZE;
+	return kpti_ng_temp_alloc;
+}
+
 static void __nocfi
 kpti_install_ng_mappings(const struct arm64_cpu_capabilities *__unused)
 {
-	typedef void (kpti_remap_fn)(int, int, phys_addr_t);
+	typedef void (kpti_remap_fn)(int, int, phys_addr_t, unsigned long);
 	extern kpti_remap_fn idmap_kpti_install_ng_mappings;
 	kpti_remap_fn *remap_fn;
 
 	int cpu = smp_processor_id();
+	int levels = CONFIG_PGTABLE_LEVELS;
+	int order = order_base_2(levels);
+	u64 kpti_ng_temp_pgd_pa = 0;
+	pgd_t *kpti_ng_temp_pgd;
+	u64 alloc = 0;
 
 	if (__this_cpu_read(this_cpu_vector) == vectors) {
 		const char *v = arm64_get_bp_hardening_vector(EL1_VECTOR_KPTI);
@@ -1671,12 +1691,40 @@ kpti_install_ng_mappings(const struct arm64_cpu_capabilities *__unused)
 
 	remap_fn = (void *)__pa_symbol(function_nocfi(idmap_kpti_install_ng_mappings));
 
+	if (!cpu) {
+		alloc = __get_free_pages(GFP_ATOMIC | __GFP_ZERO, order);
+		kpti_ng_temp_pgd = (pgd_t *)(alloc + (levels - 1) * PAGE_SIZE);
+		kpti_ng_temp_alloc = kpti_ng_temp_pgd_pa = __pa(kpti_ng_temp_pgd);
+
+		//
+		// Create a minimal page table hierarchy that permits us to map
+		// the swapper page tables temporarily as we traverse them.
+		//
+		// The physical pages are laid out as follows:
+		//
+		// +--------+-/-------+-/------ +-\\--------+
+		// :  PTE[] : | PMD[] : | PUD[] : || PGD[]  :
+		// +--------+-\-------+-\------ +-//--------+
+		//      ^
+		// The first page is mapped into this hierarchy at a PMD_SHIFT
+		// aligned virtual address, so that we can manipulate the PTE
+		// level entries while the mapping is active. The first entry
+		// covers the PTE[] page itself, the remaining entries are free
+		// to be used as a ad-hoc fixmap.
+		//
+		create_kpti_ng_temp_pgd(kpti_ng_temp_pgd, __pa(alloc),
+					KPTI_NG_TEMP_VA, PAGE_SIZE, PAGE_KERNEL,
+					kpti_ng_pgd_alloc, 0);
+	}
+
 	cpu_install_idmap();
-	remap_fn(cpu, num_online_cpus(), __pa_symbol(swapper_pg_dir));
+	remap_fn(cpu, num_online_cpus(), kpti_ng_temp_pgd_pa, KPTI_NG_TEMP_VA);
 	cpu_uninstall_idmap();
 
-	if (!cpu)
+	if (!cpu) {
+		free_pages(alloc, order);
 		arm64_use_ng_mappings = true;
+	}
 }
 #else
 static void

arch/arm64/kernel/entry.S

@@ -636,18 +636,28 @@ alternative_else_nop_endif
 	 */
 	.endm
 
-	.macro tramp_data_page	dst
-	adr_l	\dst, .entry.tramp.text
-	sub	\dst, \dst, PAGE_SIZE
-	.endm
-
-	.macro tramp_data_read_var	dst, var
-#ifdef CONFIG_RANDOMIZE_BASE
-	tramp_data_page		\dst
-	add	\dst, \dst, #:lo12:__entry_tramp_data_\var
-	ldr	\dst, [\dst]
+	.macro		tramp_data_read_var	dst, var
+#ifdef CONFIG_RELOCATABLE
+	ldr		\dst, .L__tramp_data_\var
+	.ifndef		.L__tramp_data_\var
+	.pushsection	".entry.tramp.rodata", "a", %progbits
+	.align		3
+.L__tramp_data_\var:
+	.quad		\var
+	.popsection
+	.endif
 #else
-	ldr	\dst, =\var
+	/*
+	 * As !RELOCATABLE implies !RANDOMIZE_BASE the address is always a
+	 * compile time constant (and hence not secret and not worth hiding).
+	 *
+	 * As statically allocated kernel code and data always live in the top
+	 * 47 bits of the address space we can sign-extend bit 47 and avoid an
+	 * instruction to load the upper 16 bits (which must be 0xFFFF).
+	 */
+	movz		\dst, :abs_g2_s:\var
+	movk		\dst, :abs_g1_nc:\var
+	movk		\dst, :abs_g0_nc:\var
 #endif
 	.endm
 
@@ -695,7 +705,7 @@ alternative_else_nop_endif
 	msr	vbar_el1, x30
 	isb
 	.else
-	ldr	x30, =vectors
+	adr_l	x30, vectors
 	.endif // \kpti == 1
 
 	.if	\bhb == BHB_MITIGATION_FW
@@ -764,24 +774,7 @@ SYM_CODE_END(tramp_exit_native)
 SYM_CODE_START(tramp_exit_compat)
 	tramp_exit	32
 SYM_CODE_END(tramp_exit_compat)
-
-	.ltorg
 	.popsection				// .entry.tramp.text
-#ifdef CONFIG_RANDOMIZE_BASE
-	.pushsection ".rodata", "a"
-	.align PAGE_SHIFT
-SYM_DATA_START(__entry_tramp_data_start)
-__entry_tramp_data_vectors:
-	.quad	vectors
-#ifdef CONFIG_ARM_SDE_INTERFACE
-__entry_tramp_data___sdei_asm_handler:
-	.quad	__sdei_asm_handler
-#endif /* CONFIG_ARM_SDE_INTERFACE */
-__entry_tramp_data_this_cpu_vector:
-	.quad	this_cpu_vector
-SYM_DATA_END(__entry_tramp_data_start)
-	.popsection				// .rodata
-#endif /* CONFIG_RANDOMIZE_BASE */
 #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
 
 /*
@@ -932,7 +925,6 @@ NOKPROBE(call_on_irq_stack)
  * This clobbers x4, __sdei_handler() will restore this from firmware's
  * copy.
  */
-.ltorg
 .pushsection ".entry.tramp.text", "ax"
 SYM_CODE_START(__sdei_asm_entry_trampoline)
 	mrs	x4, ttbr1_el1
@@ -967,7 +959,6 @@ SYM_CODE_START(__sdei_asm_exit_trampoline)
 1:	sdei_handler_exit exit_mode=x2
 SYM_CODE_END(__sdei_asm_exit_trampoline)
 NOKPROBE(__sdei_asm_exit_trampoline)
-	.ltorg
 .popsection		// .entry.tramp.text
 #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
 

arch/arm64/kernel/vmlinux.lds.S

@@ -115,7 +115,8 @@ jiffies = jiffies_64;
 	__entry_tramp_text_start = .;			\
 	*(.entry.tramp.text)				\
 	. = ALIGN(PAGE_SIZE);				\
-	__entry_tramp_text_end = .;
+	__entry_tramp_text_end = .;			\
+	*(.entry.tramp.rodata)
 #else
 #define TRAMP_TEXT
 #endif

arch/arm64/mm/mmu.c

@@ -388,6 +388,13 @@ static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys,
 	} while (pgdp++, addr = next, addr != end);
 }
 
+#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+extern __alias(__create_pgd_mapping)
+void create_kpti_ng_temp_pgd(pgd_t *pgdir, phys_addr_t phys, unsigned long virt,
+			     phys_addr_t size, pgprot_t prot,
+			     phys_addr_t (*pgtable_alloc)(int), int flags);
+#endif
+
 static phys_addr_t __pgd_pgtable_alloc(int shift)
 {
 	void *ptr = (void *)__get_free_page(GFP_PGTABLE_KERNEL);
@@ -665,13 +672,9 @@ static int __init map_entry_trampoline(void)
 		__set_fixmap(FIX_ENTRY_TRAMP_TEXT1 - i,
 			     pa_start + i * PAGE_SIZE, prot);
 
-	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
-		extern char __entry_tramp_data_start[];
-
-		__set_fixmap(FIX_ENTRY_TRAMP_DATA,
-			     __pa_symbol(__entry_tramp_data_start),
-			     PAGE_KERNEL_RO);
-	}
+	if (IS_ENABLED(CONFIG_RELOCATABLE))
+		__set_fixmap(FIX_ENTRY_TRAMP_TEXT1 - i,
+			     pa_start + i * PAGE_SIZE, PAGE_KERNEL_RO);
 
 	return 0;
 }

arch/arm64/mm/proc.S

@@ -14,6 +14,7 @@
 #include <asm/asm-offsets.h>
 #include <asm/asm_pointer_auth.h>
 #include <asm/hwcap.h>
+#include <asm/kernel-pgtable.h>
 #include <asm/pgtable-hwdef.h>
 #include <asm/cpufeature.h>
 #include <asm/alternative.h>
@@ -200,25 +201,51 @@ SYM_FUNC_END(idmap_cpu_replace_ttbr1)
 	.popsection
 
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+
+#define KPTI_NG_PTE_FLAGS	(PTE_ATTRINDX(MT_NORMAL) | SWAPPER_PTE_FLAGS)
+
 	.pushsection ".idmap.text", "awx"
 
-	.macro	__idmap_kpti_get_pgtable_ent, type
-	dc	cvac, cur_\()\type\()p		// Ensure any existing dirty
-	dmb	sy				// lines are written back before
-	ldr	\type, [cur_\()\type\()p]	// loading the entry
-	tbz	\type, #0, skip_\()\type	// Skip invalid and
-	tbnz	\type, #11, skip_\()\type	// non-global entries
+	.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
+	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
+	.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
 
-	.macro __idmap_kpti_put_pgtable_ent_ng, type
-	orr	\type, \type, #PTE_NG		// Same bit for blocks and pages
-	str	\type, [cur_\()\type\()p]	// Update the entry and ensure
-	dmb	sy				// that it is visible to all
-	dc	civac, cur_\()\type\()p		// CPUs.
+	/*
+	 * Dereference the current table entry and map it into the temporary
+	 * fixmap slot associated with the current level.
+	 */
+	.macro	kpti_map_pgtbl, type, level
+	str	xzr, [temp_pte, #8 * (\level + 1)]	// break before make
+	dsb	nshst
+	add	pte, temp_pte, #PAGE_SIZE * (\level + 1)
+	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)
+	orr	pte, pte, pte_flags
+	str	pte, [temp_pte, #8 * (\level + 1)]
+	dsb	nshst
 	.endm
 
 /*
- * void __kpti_install_ng_mappings(int cpu, int num_cpus, phys_addr_t swapper)
+ * void __kpti_install_ng_mappings(int cpu, int num_secondaries, phys_addr_t temp_pgd,
+ *				   unsigned long temp_pte_va)
  *
  * Called exactly once from stop_machine context by each CPU found during boot.
  */
@@ -226,8 +253,10 @@ __idmap_kpti_flag:
 	.long	1
 SYM_FUNC_START(idmap_kpti_install_ng_mappings)
 	cpu		.req	w0
+	temp_pte	.req	x0
 	num_cpus	.req	w1
-	swapper_pa	.req	x2
+	pte_flags	.req	x1
+	temp_pgd_phys	.req	x2
 	swapper_ttb	.req	x3
 	flag_ptr	.req	x4
 	cur_pgdp	.req	x5
@@ -235,16 +264,15 @@ SYM_FUNC_START(idmap_kpti_install_ng_mappings)
 	pgd		.req	x7
 	cur_pudp	.req	x8
 	end_pudp	.req	x9
-	pud		.req	x10
 	cur_pmdp	.req	x11
 	end_pmdp	.req	x12
-	pmd		.req	x13
 	cur_ptep	.req	x14
 	end_ptep	.req	x15
 	pte		.req	x16
+	valid		.req	x17
 
+	mov	x5, x3				// preserve temp_pte arg
 	mrs	swapper_ttb, ttbr1_el1
-	restore_ttbr1	swapper_ttb
 	adr	flag_ptr, __idmap_kpti_flag
 
 	cbnz	cpu, __idmap_kpti_secondary
@@ -256,98 +284,71 @@ SYM_FUNC_START(idmap_kpti_install_ng_mappings)
 	eor	w17, w17, num_cpus
 	cbnz	w17, 1b
 
-	/* We need to walk swapper, so turn off the MMU. */
-	pre_disable_mmu_workaround
-	mrs	x17, sctlr_el1
-	bic	x17, x17, #SCTLR_ELx_M
-	msr	sctlr_el1, x17
+	/* Switch to the temporary page tables on this CPU only */
+	__idmap_cpu_set_reserved_ttbr1 x8, x9
+	offset_ttbr1 temp_pgd_phys, x8
+	msr	ttbr1_el1, temp_pgd_phys
 	isb
 
+	mov	temp_pte, x5
+	mov	pte_flags, #KPTI_NG_PTE_FLAGS
+
 	/* Everybody is enjoying the idmap, so we can rewrite swapper. */
 	/* PGD */
-	mov	cur_pgdp, swapper_pa
-	add	end_pgdp, cur_pgdp, #(PTRS_PER_PGD * 8)
-do_pgd:	__idmap_kpti_get_pgtable_ent	pgd
-	tbnz	pgd, #1, walk_puds
-next_pgd:
-	__idmap_kpti_put_pgtable_ent_ng	pgd
-skip_pgd:
-	add	cur_pgdp, cur_pgdp, #8
-	cmp	cur_pgdp, end_pgdp
-	b.ne	do_pgd
-
-	/* Publish the updated tables and nuke all the TLBs */
-	dsb	sy
-	tlbi	vmalle1is
-	dsb	ish
-	isb
+	adrp		cur_pgdp, swapper_pg_dir
+	kpti_map_pgtbl	pgd, 0
+	kpti_mk_tbl_ng	pgd, PTRS_PER_PGD
 
-	/* We're done: fire up the MMU again */
-	mrs	x17, sctlr_el1
-	orr	x17, x17, #SCTLR_ELx_M
-	set_sctlr_el1	x17
+	/* Ensure all the updated entries are visible to secondary CPUs */
+	dsb	ishst
+
+	/* We're done: fire up swapper_pg_dir again */
+	__idmap_cpu_set_reserved_ttbr1 x8, x9
+	msr	ttbr1_el1, swapper_ttb
+	isb
 
 	/* Set the flag to zero to indicate that we're all done */
 	str	wzr, [flag_ptr]
 	ret
 
+.Lderef_pgd:
 	/* PUD */
-walk_puds:
-	.if CONFIG_PGTABLE_LEVELS > 3
+	.if		CONFIG_PGTABLE_LEVELS > 3
+	pud		.req	x10
 	pte_to_phys	cur_pudp, pgd
-	add	end_pudp, cur_pudp, #(PTRS_PER_PUD * 8)
-do_pud:	__idmap_kpti_get_pgtable_ent	pud
-	tbnz	pud, #1, walk_pmds
-next_pud:
-	__idmap_kpti_put_pgtable_ent_ng	pud
-skip_pud:
-	add	cur_pudp, cur_pudp, 8
-	cmp	cur_pudp, end_pudp
-	b.ne	do_pud
-	b	next_pgd
-	.else /* CONFIG_PGTABLE_LEVELS <= 3 */
-	mov	pud, pgd
-	b	walk_pmds
-next_pud:
-	b	next_pgd
+	kpti_map_pgtbl	pud, 1
+	kpti_mk_tbl_ng	pud, PTRS_PER_PUD
+	b		.Lnext_pgd
+	.else		/* CONFIG_PGTABLE_LEVELS <= 3 */
+	pud		.req	pgd
+	.set		.Lnext_pud, .Lnext_pgd
 	.endif
 
+.Lderef_pud:
 	/* PMD */
-walk_pmds:
-	.if CONFIG_PGTABLE_LEVELS > 2
+	.if		CONFIG_PGTABLE_LEVELS > 2
+	pmd		.req	x13
 	pte_to_phys	cur_pmdp, pud
-	add	end_pmdp, cur_pmdp, #(PTRS_PER_PMD * 8)
-do_pmd:	__idmap_kpti_get_pgtable_ent	pmd
-	tbnz	pmd, #1, walk_ptes
-next_pmd:
-	__idmap_kpti_put_pgtable_ent_ng	pmd
-skip_pmd:
-	add	cur_pmdp, cur_pmdp, #8
-	cmp	cur_pmdp, end_pmdp
-	b.ne	do_pmd
-	b	next_pud
-	.else /* CONFIG_PGTABLE_LEVELS <= 2 */
-	mov	pmd, pud
-	b	walk_ptes
-next_pmd:
-	b	next_pud
+	kpti_map_pgtbl	pmd, 2
+	kpti_mk_tbl_ng	pmd, PTRS_PER_PMD
+	b		.Lnext_pud
+	.else		/* CONFIG_PGTABLE_LEVELS <= 2 */
+	pmd		.req	pgd
+	.set		.Lnext_pmd, .Lnext_pgd
 	.endif
 
+.Lderef_pmd:
 	/* PTE */
-walk_ptes:
 	pte_to_phys	cur_ptep, pmd
-	add	end_ptep, cur_ptep, #(PTRS_PER_PTE * 8)
-do_pte:	__idmap_kpti_get_pgtable_ent	pte
-	__idmap_kpti_put_pgtable_ent_ng	pte
-skip_pte:
-	add	cur_ptep, cur_ptep, #8
-	cmp	cur_ptep, end_ptep
-	b.ne	do_pte
-	b	next_pmd
+	kpti_map_pgtbl	pte, 3
+	kpti_mk_tbl_ng	pte, PTRS_PER_PTE
+	b		.Lnext_pmd
 
 	.unreq	cpu
+	.unreq	temp_pte
 	.unreq	num_cpus
-	.unreq	swapper_pa
+	.unreq	pte_flags
+	.unreq	temp_pgd_phys
 	.unreq	cur_pgdp
 	.unreq	end_pgdp
 	.unreq	pgd
@@ -360,6 +361,7 @@ skip_pte:
 	.unreq	cur_ptep
 	.unreq	end_ptep
 	.unreq	pte
+	.unreq	valid
 
 	/* Secondary CPUs end up here */
 __idmap_kpti_secondary:
@@ -379,7 +381,6 @@ __idmap_kpti_secondary:
 	cbnz	w16, 1b
 
 	/* All done, act like nothing happened */
-	offset_ttbr1 swapper_ttb, x16
 	msr	ttbr1_el1, swapper_ttb
 	isb
 	ret