Merge tag 'x86_alternatives_for_v6.10_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 asm alternatives updates from Borislav Petkov:

 - Switch the in-place instruction patching which lead to at least one
   weird bug with 32-bit guests, seeing stale instruction bytes, to one
   working on a buffer, like the rest of the alternatives code does

 - Add a long overdue check to the X86_FEATURE flag modifying functions
   to warn when former get changed in a non-compatible way after
   alternatives have been patched because those changes will be already
   wrong

 - Other cleanups

* tag 'x86_alternatives_for_v6.10_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/alternatives: Remove alternative_input_2()
  x86/alternatives: Sort local vars in apply_alternatives()
  x86/alternatives: Optimize optimize_nops()
  x86/alternatives: Get rid of __optimize_nops()
  x86/alternatives: Use a temporary buffer when optimizing NOPs
  x86/alternatives: Catch late X86_FEATURE modifiers

3 files changed, 64 insertions, 81 deletions

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 45a280f2161c..7555c15b7183 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -125,6 +125,20 @@ const unsigned char * const x86_nops[ASM_NOP_MAX+1] =
 };
 
 /*
+ * Nomenclature for variable names to simplify and clarify this code and ease
+ * any potential staring at it:
+ *
+ * @instr: source address of the original instructions in the kernel text as
+ * generated by the compiler.
+ *
+ * @buf: temporary buffer on which the patching operates. This buffer is
+ * eventually text-poked into the kernel image.
+ *
+ * @replacement/@repl: pointer to the opcodes which are replacing @instr, located
+ * in the .altinstr_replacement section.
+ */
+
+/*
  * Fill the buffer with a single effective instruction of size @len.
  *
  * In order not to issue an ORC stack depth tracking CFI entry (Call Frame Info)
@@ -133,28 +147,28 @@ const unsigned char * const x86_nops[ASM_NOP_MAX+1] =
  * each single-byte NOPs). If @len to fill out is > ASM_NOP_MAX, pad with INT3 and
  * *jump* over instead of executing long and daft NOPs.
  */
-static void add_nop(u8 *instr, unsigned int len)
+static void add_nop(u8 *buf, unsigned int len)
 {
-	u8 *target = instr + len;
+	u8 *target = buf + len;
 
 	if (!len)
 		return;
 
 	if (len <= ASM_NOP_MAX) {
-		memcpy(instr, x86_nops[len], len);
+		memcpy(buf, x86_nops[len], len);
 		return;
 	}
 
 	if (len < 128) {
-		__text_gen_insn(instr, JMP8_INSN_OPCODE, instr, target, JMP8_INSN_SIZE);
-		instr += JMP8_INSN_SIZE;
+		__text_gen_insn(buf, JMP8_INSN_OPCODE, buf, target, JMP8_INSN_SIZE);
+		buf += JMP8_INSN_SIZE;
 	} else {
-		__text_gen_insn(instr, JMP32_INSN_OPCODE, instr, target, JMP32_INSN_SIZE);
-		instr += JMP32_INSN_SIZE;
+		__text_gen_insn(buf, JMP32_INSN_OPCODE, buf, target, JMP32_INSN_SIZE);
+		buf += JMP32_INSN_SIZE;
 	}
 
-	for (;instr < target; instr++)
-		*instr = INT3_INSN_OPCODE;
+	for (;buf < target; buf++)
+		*buf = INT3_INSN_OPCODE;
 }
 
 extern s32 __retpoline_sites[], __retpoline_sites_end[];
@@ -187,12 +201,12 @@ static bool insn_is_nop(struct insn *insn)
  * Find the offset of the first non-NOP instruction starting at @offset
  * but no further than @len.
  */
-static int skip_nops(u8 *instr, int offset, int len)
+static int skip_nops(u8 *buf, int offset, int len)
 {
 	struct insn insn;
 
 	for (; offset < len; offset += insn.length) {
-		if (insn_decode_kernel(&insn, &instr[offset]))
+		if (insn_decode_kernel(&insn, &buf[offset]))
 			break;
 
 		if (!insn_is_nop(&insn))
@@ -203,66 +217,32 @@ static int skip_nops(u8 *instr, int offset, int len)
 }
 
 /*
- * Optimize a sequence of NOPs, possibly preceded by an unconditional jump
- * to the end of the NOP sequence into a single NOP.
- */
-static bool
-__optimize_nops(u8 *instr, size_t len, struct insn *insn, int *next, int *prev, int *target)
-{
-	int i = *next - insn->length;
-
-	switch (insn->opcode.bytes[0]) {
-	case JMP8_INSN_OPCODE:
-	case JMP32_INSN_OPCODE:
-		*prev = i;
-		*target = *next + insn->immediate.value;
-		return false;
-	}
-
-	if (insn_is_nop(insn)) {
-		int nop = i;
-
-		*next = skip_nops(instr, *next, len);
-		if (*target && *next == *target)
-			nop = *prev;
-
-		add_nop(instr + nop, *next - nop);
-		DUMP_BYTES(ALT, instr, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, *next);
-		return true;
-	}
-
-	*target = 0;
-	return false;
-}
-
-/*
  * "noinline" to cause control flow change and thus invalidate I$ and
  * cause refetch after modification.
  */
-static void __init_or_module noinline optimize_nops(u8 *instr, size_t len)
+static void noinline optimize_nops(const u8 * const instr, u8 *buf, size_t len)
 {
-	int prev, target = 0;
-
 	for (int next, i = 0; i < len; i = next) {
 		struct insn insn;
 
-		if (insn_decode_kernel(&insn, &instr[i]))
+		if (insn_decode_kernel(&insn, &buf[i]))
 			return;
 
 		next = i + insn.length;
 
-		__optimize_nops(instr, len, &insn, &next, &prev, &target);
-	}
-}
+		if (insn_is_nop(&insn)) {
+			int nop = i;
 
-static void __init_or_module noinline optimize_nops_inplace(u8 *instr, size_t len)
-{
-	unsigned long flags;
+			/* Has the NOP already been optimized? */
+			if (i + insn.length == len)
+				return;
 
-	local_irq_save(flags);
-	optimize_nops(instr, len);
-	sync_core();
-	local_irq_restore(flags);
+			next = skip_nops(buf, next, len);
+
+			add_nop(buf + nop, next - nop);
+			DUMP_BYTES(ALT, buf, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, next);
+		}
+	}
 }
 
 /*
@@ -335,11 +315,9 @@ bool need_reloc(unsigned long offset, u8 *src, size_t src_len)
 	return (target < src || target > src + src_len);
 }
 
-void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
+static void __apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl, size_t repl_len)
 {
-	int prev, target = 0;
-
-	for (int next, i = 0; i < len; i = next) {
+	for (int next, i = 0; i < instrlen; i = next) {
 		struct insn insn;
 
 		if (WARN_ON_ONCE(insn_decode_kernel(&insn, &buf[i])))
@@ -347,9 +325,6 @@ void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 
 		next = i + insn.length;
 
-		if (__optimize_nops(buf, len, &insn, &next, &prev, &target))
-			continue;
-
 		switch (insn.opcode.bytes[0]) {
 		case 0x0f:
 			if (insn.opcode.bytes[1] < 0x80 ||
@@ -361,10 +336,10 @@ void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 		case JMP8_INSN_OPCODE:
 		case JMP32_INSN_OPCODE:
 		case CALL_INSN_OPCODE:
-			if (need_reloc(next + insn.immediate.value, src, src_len)) {
+			if (need_reloc(next + insn.immediate.value, repl, repl_len)) {
 				apply_reloc(insn.immediate.nbytes,
 					    buf + i + insn_offset_immediate(&insn),
-					    src - dest);
+					    repl - instr);
 			}
 
 			/*
@@ -372,7 +347,7 @@ void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 			 */
 			if (insn.opcode.bytes[0] == JMP32_INSN_OPCODE) {
 				s32 imm = insn.immediate.value;
-				imm += src - dest;
+				imm += repl - instr;
 				imm += JMP32_INSN_SIZE - JMP8_INSN_SIZE;
 				if ((imm >> 31) == (imm >> 7)) {
 					buf[i+0] = JMP8_INSN_OPCODE;
@@ -385,15 +360,21 @@ void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 		}
 
 		if (insn_rip_relative(&insn)) {
-			if (need_reloc(next + insn.displacement.value, src, src_len)) {
+			if (need_reloc(next + insn.displacement.value, repl, repl_len)) {
 				apply_reloc(insn.displacement.nbytes,
 					    buf + i + insn_offset_displacement(&insn),
-					    src - dest);
+					    repl - instr);
 			}
 		}
 	}
 }
 
+void apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl, size_t repl_len)
+{
+	__apply_relocation(buf, instr, instrlen, repl, repl_len);
+	optimize_nops(instr, buf, repl_len);
+}
+
 /* Low-level backend functions usable from alternative code replacements. */
 DEFINE_ASM_FUNC(nop_func, "", .entry.text);
 EXPORT_SYMBOL_GPL(nop_func);
@@ -464,9 +445,9 @@ static int alt_replace_call(u8 *instr, u8 *insn_buff, struct alt_instr *a)
 void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 						  struct alt_instr *end)
 {
-	struct alt_instr *a;
-	u8 *instr, *replacement;
 	u8 insn_buff[MAX_PATCH_LEN];
+	u8 *instr, *replacement;
+	struct alt_instr *a;
 
 	DPRINTK(ALT, "alt table %px, -> %px", start, end);
 
@@ -504,7 +485,9 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 		 *   patch if feature is *NOT* present.
 		 */
 		if (!boot_cpu_has(a->cpuid) == !(a->flags & ALT_FLAG_NOT)) {
-			optimize_nops_inplace(instr, a->instrlen);
+			memcpy(insn_buff, instr, a->instrlen);
+			optimize_nops(instr, insn_buff, a->instrlen);
+			text_poke_early(instr, insn_buff, a->instrlen);
 			continue;
 		}
 
@@ -526,7 +509,7 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 		for (; insn_buff_sz < a->instrlen; insn_buff_sz++)
 			insn_buff[insn_buff_sz] = 0x90;
 
-		apply_relocation(insn_buff, a->instrlen, instr, replacement, a->replacementlen);
+		apply_relocation(insn_buff, instr, a->instrlen, replacement, a->replacementlen);
 
 		DUMP_BYTES(ALT, instr, a->instrlen, "%px:   old_insn: ", instr);
 		DUMP_BYTES(ALT, replacement, a->replacementlen, "%px:   rpl_insn: ", replacement);
@@ -761,7 +744,7 @@ void __init_or_module noinline apply_retpolines(s32 *start, s32 *end)
 
 		len = patch_retpoline(addr, &insn, bytes);
 		if (len == insn.length) {
-			optimize_nops(bytes, len);
+			optimize_nops(addr, bytes, len);
 			DUMP_BYTES(RETPOLINE, ((u8*)addr),  len, "%px: orig: ", addr);
 			DUMP_BYTES(RETPOLINE, ((u8*)bytes), len, "%px: repl: ", addr);
 			text_poke_early(addr, bytes, len);
diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
index e92ff0c11db8..465647456753 100644
--- a/arch/x86/kernel/callthunks.c
+++ b/arch/x86/kernel/callthunks.c
@@ -185,8 +185,7 @@ static void *patch_dest(void *dest, bool direct)
 	u8 *pad = dest - tsize;
 
 	memcpy(insn_buff, skl_call_thunk_template, tsize);
-	apply_relocation(insn_buff, tsize, pad,
-			 skl_call_thunk_template, tsize);
+	apply_relocation(insn_buff, pad, tsize, skl_call_thunk_template, tsize);
 
 	/* Already patched? */
 	if (!bcmp(pad, insn_buff, tsize))
@@ -308,8 +307,7 @@ static bool is_callthunk(void *addr)
 	pad = (void *)(dest - tmpl_size);
 
 	memcpy(insn_buff, skl_call_thunk_template, tmpl_size);
-	apply_relocation(insn_buff, tmpl_size, pad,
-			 skl_call_thunk_template, tmpl_size);
+	apply_relocation(insn_buff, pad, tmpl_size, skl_call_thunk_template, tmpl_size);
 
 	return !bcmp(pad, insn_buff, tmpl_size);
 }
@@ -327,8 +325,7 @@ int x86_call_depth_emit_accounting(u8 **pprog, void *func, void *ip)
 		return 0;
 
 	memcpy(insn_buff, skl_call_thunk_template, tmpl_size);
-	apply_relocation(insn_buff, tmpl_size, ip,
-			 skl_call_thunk_template, tmpl_size);
+	apply_relocation(insn_buff, ip, tmpl_size, skl_call_thunk_template, tmpl_size);
 
 	memcpy(*pprog, insn_buff, tmpl_size);
 	*pprog += tmpl_size;
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index 946813d816bf..b7d9f530ae16 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -114,6 +114,9 @@ static void do_clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int feature)
 	if (WARN_ON(feature >= MAX_FEATURE_BITS))
 		return;
 
+	if (boot_cpu_has(feature))
+		WARN_ON(alternatives_patched);
+
 	clear_feature(c, feature);
 
 	/* Collect all features to disable, handling dependencies */