arm64 fixes for -rc4

- Disable software tag-based KASAN when compiling with GCC, as functions
   are incorrectly instrumented leading to a crash early during boot.
 
 - Fix pkey configuration for kernel threads when POE is enabled.
 
 - Fix invalid memory accesses in uprobes when targetting load-literal
   instructions.
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Merge tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux

Pull arm64 fixes from Will Deacon:

 - Disable software tag-based KASAN when compiling with GCC, as
   functions are incorrectly instrumented leading to a crash early
   during boot

 - Fix pkey configuration for kernel threads when POE is enabled

 - Fix invalid memory accesses in uprobes when targetting load-literal
   instructions

* tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux:
  kasan: Disable Software Tag-Based KASAN with GCC
  Documentation/protection-keys: add AArch64 to documentation
  arm64: set POR_EL0 for kernel threads
  arm64: probes: Fix uprobes for big-endian kernels
  arm64: probes: Fix simulate_ldr*_literal()
  arm64: probes: Remove broken LDR (literal) uprobe support

Documentation/core-api/protection-keys.rst

@@ -12,7 +12,10 @@ Pkeys Userspace (PKU) is a feature which can be found on:
         * Intel server CPUs, Skylake and later
         * Intel client CPUs, Tiger Lake (11th Gen Core) and later
         * Future AMD CPUs
+        * arm64 CPUs implementing the Permission Overlay Extension (FEAT_S1POE)
 
+x86_64
+======
 Pkeys work by dedicating 4 previously Reserved bits in each page table entry to
 a "protection key", giving 16 possible keys.
 
@@ -28,6 +31,22 @@ register.  The feature is only available in 64-bit mode, even though there is
 theoretically space in the PAE PTEs.  These permissions are enforced on data
 access only and have no effect on instruction fetches.
 
+arm64
+=====
+
+Pkeys use 3 bits in each page table entry, to encode a "protection key index",
+giving 8 possible keys.
+
+Protections for each key are defined with a per-CPU user-writable system
+register (POR_EL0).  This is a 64-bit register encoding read, write and execute
+overlay permissions for each protection key index.
+
+Being a CPU register, POR_EL0 is inherently thread-local, potentially giving
+each thread a different set of protections from every other thread.
+
+Unlike x86_64, the protection key permissions also apply to instruction
+fetches.
+
 Syscalls
 ========
 
@@ -38,11 +57,10 @@ There are 3 system calls which directly interact with pkeys::
 	int pkey_mprotect(unsigned long start, size_t len,
 			  unsigned long prot, int pkey);
 
-Before a pkey can be used, it must first be allocated with
-pkey_alloc().  An application calls the WRPKRU instruction
-directly in order to change access permissions to memory covered
-with a key.  In this example WRPKRU is wrapped by a C function
-called pkey_set().
+Before a pkey can be used, it must first be allocated with pkey_alloc().  An
+application writes to the architecture specific CPU register directly in order
+to change access permissions to memory covered with a key.  In this example
+this is wrapped by a C function called pkey_set().
 ::
 
 	int real_prot = PROT_READ|PROT_WRITE;
@@ -64,9 +82,9 @@ is no longer in use::
 	munmap(ptr, PAGE_SIZE);
 	pkey_free(pkey);
 
-.. note:: pkey_set() is a wrapper for the RDPKRU and WRPKRU instructions.
-          An example implementation can be found in
-          tools/testing/selftests/x86/protection_keys.c.
+.. note:: pkey_set() is a wrapper around writing to the CPU register.
+          Example implementations can be found in
+          tools/testing/selftests/mm/pkey-{arm64,powerpc,x86}.h
 
 Behavior
 ========
@@ -96,3 +114,7 @@ with a read()::
 The kernel will send a SIGSEGV in both cases, but si_code will be set
 to SEGV_PKERR when violating protection keys versus SEGV_ACCERR when
 the plain mprotect() permissions are violated.
+
+Note that kernel accesses from a kthread (such as io_uring) will use a default
+value for the protection key register and so will not be consistent with
+userspace's value of the register or mprotect().

arch/arm64/include/asm/uprobes.h

@@ -10,11 +10,9 @@
 #include <asm/insn.h>
 #include <asm/probes.h>
 
-#define MAX_UINSN_BYTES		AARCH64_INSN_SIZE
-
 #define UPROBE_SWBP_INSN	cpu_to_le32(BRK64_OPCODE_UPROBES)
 #define UPROBE_SWBP_INSN_SIZE	AARCH64_INSN_SIZE
-#define UPROBE_XOL_SLOT_BYTES	MAX_UINSN_BYTES
+#define UPROBE_XOL_SLOT_BYTES	AARCH64_INSN_SIZE
 
 typedef __le32 uprobe_opcode_t;
 
@@ -23,8 +21,8 @@ struct arch_uprobe_task {
 
 struct arch_uprobe {
 	union {
-		u8 insn[MAX_UINSN_BYTES];
-		u8 ixol[MAX_UINSN_BYTES];
+		__le32 insn;
+		__le32 ixol;
 	};
 	struct arch_probe_insn api;
 	bool simulate;

arch/arm64/kernel/probes/decode-insn.c

@@ -99,10 +99,6 @@ arm_probe_decode_insn(probe_opcode_t insn, struct arch_probe_insn *api)
 	    aarch64_insn_is_blr(insn) ||
 	    aarch64_insn_is_ret(insn)) {
 		api->handler = simulate_br_blr_ret;
-	} else if (aarch64_insn_is_ldr_lit(insn)) {
-		api->handler = simulate_ldr_literal;
-	} else if (aarch64_insn_is_ldrsw_lit(insn)) {
-		api->handler = simulate_ldrsw_literal;
 	} else {
 		/*
 		 * Instruction cannot be stepped out-of-line and we don't
@@ -140,6 +136,17 @@ arm_kprobe_decode_insn(kprobe_opcode_t *addr, struct arch_specific_insn *asi)
 	probe_opcode_t insn = le32_to_cpu(*addr);
 	probe_opcode_t *scan_end = NULL;
 	unsigned long size = 0, offset = 0;
+	struct arch_probe_insn *api = &asi->api;
+
+	if (aarch64_insn_is_ldr_lit(insn)) {
+		api->handler = simulate_ldr_literal;
+		decoded = INSN_GOOD_NO_SLOT;
+	} else if (aarch64_insn_is_ldrsw_lit(insn)) {
+		api->handler = simulate_ldrsw_literal;
+		decoded = INSN_GOOD_NO_SLOT;
+	} else {
+		decoded = arm_probe_decode_insn(insn, &asi->api);
+	}
 
 	/*
 	 * If there's a symbol defined in front of and near enough to
@@ -157,7 +164,6 @@ arm_kprobe_decode_insn(kprobe_opcode_t *addr, struct arch_specific_insn *asi)
 		else
 			scan_end = addr - MAX_ATOMIC_CONTEXT_SIZE;
 	}
-	decoded = arm_probe_decode_insn(insn, &asi->api);
 
 	if (decoded != INSN_REJECTED && scan_end)
 		if (is_probed_address_atomic(addr - 1, scan_end))

arch/arm64/kernel/probes/simulate-insn.c

@@ -171,17 +171,15 @@ simulate_tbz_tbnz(u32 opcode, long addr, struct pt_regs *regs)
 void __kprobes
 simulate_ldr_literal(u32 opcode, long addr, struct pt_regs *regs)
 {
-	u64 *load_addr;
+	unsigned long load_addr;
 	int xn = opcode & 0x1f;
-	int disp;
 
-	disp = ldr_displacement(opcode);
-	load_addr = (u64 *) (addr + disp);
+	load_addr = addr + ldr_displacement(opcode);
 
 	if (opcode & (1 << 30))	/* x0-x30 */
-		set_x_reg(regs, xn, *load_addr);
+		set_x_reg(regs, xn, READ_ONCE(*(u64 *)load_addr));
 	else			/* w0-w30 */
-		set_w_reg(regs, xn, *load_addr);
+		set_w_reg(regs, xn, READ_ONCE(*(u32 *)load_addr));
 
 	instruction_pointer_set(regs, instruction_pointer(regs) + 4);
 }
@@ -189,14 +187,12 @@ simulate_ldr_literal(u32 opcode, long addr, struct pt_regs *regs)
 void __kprobes
 simulate_ldrsw_literal(u32 opcode, long addr, struct pt_regs *regs)
 {
-	s32 *load_addr;
+	unsigned long load_addr;
 	int xn = opcode & 0x1f;
-	int disp;
 
-	disp = ldr_displacement(opcode);
-	load_addr = (s32 *) (addr + disp);
+	load_addr = addr + ldr_displacement(opcode);
 
-	set_x_reg(regs, xn, *load_addr);
+	set_x_reg(regs, xn, READ_ONCE(*(s32 *)load_addr));
 
 	instruction_pointer_set(regs, instruction_pointer(regs) + 4);
 }

arch/arm64/kernel/probes/uprobes.c

@@ -42,7 +42,7 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
 	else if (!IS_ALIGNED(addr, AARCH64_INSN_SIZE))
 		return -EINVAL;
 
-	insn = *(probe_opcode_t *)(&auprobe->insn[0]);
+	insn = le32_to_cpu(auprobe->insn);
 
 	switch (arm_probe_decode_insn(insn, &auprobe->api)) {
 	case INSN_REJECTED:
@@ -108,7 +108,7 @@ bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
 	if (!auprobe->simulate)
 		return false;
 
-	insn = *(probe_opcode_t *)(&auprobe->insn[0]);
+	insn = le32_to_cpu(auprobe->insn);
 	addr = instruction_pointer(regs);
 
 	if (auprobe->api.handler)

arch/arm64/kernel/process.c

@@ -412,6 +412,9 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 
 		p->thread.cpu_context.x19 = (unsigned long)args->fn;
 		p->thread.cpu_context.x20 = (unsigned long)args->fn_arg;
+
+		if (system_supports_poe())
+			p->thread.por_el0 = POR_EL0_INIT;
 	}
 	p->thread.cpu_context.pc = (unsigned long)ret_from_fork;
 	p->thread.cpu_context.sp = (unsigned long)childregs;

lib/Kconfig.kasan

@@ -22,8 +22,11 @@ config ARCH_DISABLE_KASAN_INLINE
 config CC_HAS_KASAN_GENERIC
 	def_bool $(cc-option, -fsanitize=kernel-address)
 
+# GCC appears to ignore no_sanitize_address when -fsanitize=kernel-hwaddress
+# is passed. See https://bugzilla.kernel.org/show_bug.cgi?id=218854 (and
+# the linked LKML thread) for more details.
 config CC_HAS_KASAN_SW_TAGS
-	def_bool $(cc-option, -fsanitize=kernel-hwaddress)
+	def_bool !CC_IS_GCC && $(cc-option, -fsanitize=kernel-hwaddress)
 
 # This option is only required for software KASAN modes.
 # Old GCC versions do not have proper support for no_sanitize_address.
@@ -98,7 +101,7 @@ config KASAN_SW_TAGS
 	help
 	  Enables Software Tag-Based KASAN.
 
-	  Requires GCC 11+ or Clang.
+	  Requires Clang.
 
 	  Supported only on arm64 CPUs and relies on Top Byte Ignore.