x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 581 insertions, 0 deletions

diff --git a/scripts/kconfig/preprocess.c b/scripts/kconfig/preprocess.c
new file mode 100644
index 000000000..783abcaa5
--- /dev/null
+++ b/scripts/kconfig/preprocess.c
@@ -0,0 +1,581 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Copyright (C) 2018 Masahiro Yamada <yamada.masahiro@socionext.com>
+
+#include <ctype.h>
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <array_size.h>
+#include <list.h>
+#include <xalloc.h>
+#include "internal.h"
+#include "lkc.h"
+#include "preprocess.h"
+
+static char *expand_string_with_args(const char *in, int argc, char *argv[]);
+static char *expand_string(const char *in);
+
+static void __attribute__((noreturn)) pperror(const char *format, ...)
+{
+	va_list ap;
+
+	fprintf(stderr, "%s:%d: ", cur_filename, yylineno);
+	va_start(ap, format);
+	vfprintf(stderr, format, ap);
+	va_end(ap);
+	fprintf(stderr, "\n");
+
+	exit(1);
+}
+
+/*
+ * Environment variables
+ */
+static LIST_HEAD(env_list);
+
+struct env {
+	char *name;
+	char *value;
+	struct list_head node;
+};
+
+static void env_add(const char *name, const char *value)
+{
+	struct env *e;
+
+	e = xmalloc(sizeof(*e));
+	e->name = xstrdup(name);
+	e->value = xstrdup(value);
+
+	list_add_tail(&e->node, &env_list);
+}
+
+static void env_del(struct env *e)
+{
+	list_del(&e->node);
+	free(e->name);
+	free(e->value);
+	free(e);
+}
+
+/* The returned pointer must be freed when done */
+static char *env_expand(const char *name)
+{
+	struct env *e;
+	const char *value;
+
+	if (!*name)
+		return NULL;
+
+	list_for_each_entry(e, &env_list, node) {
+		if (!strcmp(name, e->name))
+			return xstrdup(e->value);
+	}
+
+	value = getenv(name);
+	if (!value)
+		return NULL;
+
+	/*
+	 * We need to remember all referenced environment variables.
+	 * They will be written out to include/config/auto.conf.cmd
+	 */
+	env_add(name, value);
+
+	return xstrdup(value);
+}
+
+void env_write_dep(struct gstr *s)
+{
+	struct env *e, *tmp;
+
+	list_for_each_entry_safe(e, tmp, &env_list, node) {
+		str_printf(s,
+			   "\n"
+			   "ifneq \"$(%s)\" \"%s\"\n"
+			   "$(autoconfig): FORCE\n"
+			   "endif\n",
+			   e->name, e->value);
+		env_del(e);
+	}
+}
+
+/*
+ * Built-in functions
+ */
+struct function {
+	const char *name;
+	unsigned int min_args;
+	unsigned int max_args;
+	char *(*func)(int argc, char *argv[]);
+};
+
+static char *do_error_if(int argc, char *argv[])
+{
+	if (!strcmp(argv[0], "y"))
+		pperror("%s", argv[1]);
+
+	return xstrdup("");
+}
+
+static char *do_filename(int argc, char *argv[])
+{
+	return xstrdup(cur_filename);
+}
+
+static char *do_info(int argc, char *argv[])
+{
+	printf("%s\n", argv[0]);
+
+	return xstrdup("");
+}
+
+static char *do_lineno(int argc, char *argv[])
+{
+	char buf[16];
+
+	sprintf(buf, "%d", yylineno);
+
+	return xstrdup(buf);
+}
+
+static char *do_shell(int argc, char *argv[])
+{
+	FILE *p;
+	char buf[4096];
+	char *cmd;
+	size_t nread;
+	int i;
+
+	cmd = argv[0];
+
+	p = popen(cmd, "r");
+	if (!p) {
+		perror(cmd);
+		exit(1);
+	}
+
+	nread = fread(buf, 1, sizeof(buf), p);
+	if (nread == sizeof(buf))
+		nread--;
+
+	/* remove trailing new lines */
+	while (nread > 0 && buf[nread - 1] == '\n')
+		nread--;
+
+	buf[nread] = 0;
+
+	/* replace a new line with a space */
+	for (i = 0; i < nread; i++) {
+		if (buf[i] == '\n')
+			buf[i] = ' ';
+	}
+
+	if (pclose(p) == -1) {
+		perror(cmd);
+		exit(1);
+	}
+
+	return xstrdup(buf);
+}
+
+static char *do_warning_if(int argc, char *argv[])
+{
+	if (!strcmp(argv[0], "y"))
+		fprintf(stderr, "%s:%d: %s\n", cur_filename, yylineno, argv[1]);
+
+	return xstrdup("");
+}
+
+static const struct function function_table[] = {
+	/* Name		MIN	MAX	Function */
+	{ "error-if",	2,	2,	do_error_if },
+	{ "filename",	0,	0,	do_filename },
+	{ "info",	1,	1,	do_info },
+	{ "lineno",	0,	0,	do_lineno },
+	{ "shell",	1,	1,	do_shell },
+	{ "warning-if",	2,	2,	do_warning_if },
+};
+
+#define FUNCTION_MAX_ARGS		16
+
+static char *function_expand(const char *name, int argc, char *argv[])
+{
+	const struct function *f;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(function_table); i++) {
+		f = &function_table[i];
+		if (strcmp(f->name, name))
+			continue;
+
+		if (argc < f->min_args)
+			pperror("too few function arguments passed to '%s'",
+				name);
+
+		if (argc > f->max_args)
+			pperror("too many function arguments passed to '%s'",
+				name);
+
+		return f->func(argc, argv);
+	}
+
+	return NULL;
+}
+
+/*
+ * Variables (and user-defined functions)
+ */
+static LIST_HEAD(variable_list);
+
+struct variable {
+	char *name;
+	char *value;
+	enum variable_flavor flavor;
+	int exp_count;
+	struct list_head node;
+};
+
+static struct variable *variable_lookup(const char *name)
+{
+	struct variable *v;
+
+	list_for_each_entry(v, &variable_list, node) {
+		if (!strcmp(name, v->name))
+			return v;
+	}
+
+	return NULL;
+}
+
+static char *variable_expand(const char *name, int argc, char *argv[])
+{
+	struct variable *v;
+	char *res;
+
+	v = variable_lookup(name);
+	if (!v)
+		return NULL;
+
+	if (argc == 0 && v->exp_count)
+		pperror("Recursive variable '%s' references itself (eventually)",
+			name);
+
+	if (v->exp_count > 1000)
+		pperror("Too deep recursive expansion");
+
+	v->exp_count++;
+
+	if (v->flavor == VAR_RECURSIVE)
+		res = expand_string_with_args(v->value, argc, argv);
+	else
+		res = xstrdup(v->value);
+
+	v->exp_count--;
+
+	return res;
+}
+
+void variable_add(const char *name, const char *value,
+		  enum variable_flavor flavor)
+{
+	struct variable *v;
+	char *new_value;
+	bool append = false;
+
+	v = variable_lookup(name);
+	if (v) {
+		/* For defined variables, += inherits the existing flavor */
+		if (flavor == VAR_APPEND) {
+			flavor = v->flavor;
+			append = true;
+		} else {
+			free(v->value);
+		}
+	} else {
+		/* For undefined variables, += assumes the recursive flavor */
+		if (flavor == VAR_APPEND)
+			flavor = VAR_RECURSIVE;
+
+		v = xmalloc(sizeof(*v));
+		v->name = xstrdup(name);
+		v->exp_count = 0;
+		list_add_tail(&v->node, &variable_list);
+	}
+
+	v->flavor = flavor;
+
+	if (flavor == VAR_SIMPLE)
+		new_value = expand_string(value);
+	else
+		new_value = xstrdup(value);
+
+	if (append) {
+		v->value = xrealloc(v->value,
+				    strlen(v->value) + strlen(new_value) + 2);
+		strcat(v->value, " ");
+		strcat(v->value, new_value);
+		free(new_value);
+	} else {
+		v->value = new_value;
+	}
+}
+
+static void variable_del(struct variable *v)
+{
+	list_del(&v->node);
+	free(v->name);
+	free(v->value);
+	free(v);
+}
+
+void variable_all_del(void)
+{
+	struct variable *v, *tmp;
+
+	list_for_each_entry_safe(v, tmp, &variable_list, node)
+		variable_del(v);
+}
+
+/*
+ * Evaluate a clause with arguments.  argc/argv are arguments from the upper
+ * function call.
+ *
+ * Returned string must be freed when done
+ */
+static char *eval_clause(const char *str, size_t len, int argc, char *argv[])
+{
+	char *tmp, *name, *res, *endptr, *prev, *p;
+	int new_argc = 0;
+	char *new_argv[FUNCTION_MAX_ARGS];
+	int nest = 0;
+	int i;
+	unsigned long n;
+
+	tmp = xstrndup(str, len);
+
+	/*
+	 * If variable name is '1', '2', etc.  It is generally an argument
+	 * from a user-function call (i.e. local-scope variable).  If not
+	 * available, then look-up global-scope variables.
+	 */
+	n = strtoul(tmp, &endptr, 10);
+	if (!*endptr && n > 0 && n <= argc) {
+		res = xstrdup(argv[n - 1]);
+		goto free_tmp;
+	}
+
+	prev = p = tmp;
+
+	/*
+	 * Split into tokens
+	 * The function name and arguments are separated by a comma.
+	 * For example, if the function call is like this:
+	 *   $(foo,$(x),$(y))
+	 *
+	 * The input string for this helper should be:
+	 *   foo,$(x),$(y)
+	 *
+	 * and split into:
+	 *   new_argv[0] = 'foo'
+	 *   new_argv[1] = '$(x)'
+	 *   new_argv[2] = '$(y)'
+	 */
+	while (*p) {
+		if (nest == 0 && *p == ',') {
+			*p = 0;
+			if (new_argc >= FUNCTION_MAX_ARGS)
+				pperror("too many function arguments");
+			new_argv[new_argc++] = prev;
+			prev = p + 1;
+		} else if (*p == '(') {
+			nest++;
+		} else if (*p == ')') {
+			nest--;
+		}
+
+		p++;
+	}
+
+	if (new_argc >= FUNCTION_MAX_ARGS)
+		pperror("too many function arguments");
+	new_argv[new_argc++] = prev;
+
+	/*
+	 * Shift arguments
+	 * new_argv[0] represents a function name or a variable name.  Put it
+	 * into 'name', then shift the rest of the arguments.  This simplifies
+	 * 'const' handling.
+	 */
+	name = expand_string_with_args(new_argv[0], argc, argv);
+	new_argc--;
+	for (i = 0; i < new_argc; i++)
+		new_argv[i] = expand_string_with_args(new_argv[i + 1],
+						      argc, argv);
+
+	/* Search for variables */
+	res = variable_expand(name, new_argc, new_argv);
+	if (res)
+		goto free;
+
+	/* Look for built-in functions */
+	res = function_expand(name, new_argc, new_argv);
+	if (res)
+		goto free;
+
+	/* Last, try environment variable */
+	if (new_argc == 0) {
+		res = env_expand(name);
+		if (res)
+			goto free;
+	}
+
+	res = xstrdup("");
+free:
+	for (i = 0; i < new_argc; i++)
+		free(new_argv[i]);
+	free(name);
+free_tmp:
+	free(tmp);
+
+	return res;
+}
+
+/*
+ * Expand a string that follows '$'
+ *
+ * For example, if the input string is
+ *     ($(FOO)$($(BAR)))$(BAZ)
+ * this helper evaluates
+ *     $($(FOO)$($(BAR)))
+ * and returns a new string containing the expansion (note that the string is
+ * recursively expanded), also advancing 'str' to point to the next character
+ * after the corresponding closing parenthesis, in this case, *str will be
+ *     $(BAR)
+ */
+static char *expand_dollar_with_args(const char **str, int argc, char *argv[])
+{
+	const char *p = *str;
+	const char *q;
+	int nest = 0;
+
+	/*
+	 * In Kconfig, variable/function references always start with "$(".
+	 * Neither single-letter variables as in $A nor curly braces as in ${CC}
+	 * are supported.  '$' not followed by '(' loses its special meaning.
+	 */
+	if (*p != '(') {
+		*str = p;
+		return xstrdup("$");
+	}
+
+	p++;
+	q = p;
+	while (*q) {
+		if (*q == '(') {
+			nest++;
+		} else if (*q == ')') {
+			if (nest-- == 0)
+				break;
+		}
+		q++;
+	}
+
+	if (!*q)
+		pperror("unterminated reference to '%s': missing ')'", p);
+
+	/* Advance 'str' to after the expanded initial portion of the string */
+	*str = q + 1;
+
+	return eval_clause(p, q - p, argc, argv);
+}
+
+char *expand_dollar(const char **str)
+{
+	return expand_dollar_with_args(str, 0, NULL);
+}
+
+static char *__expand_string(const char **str, bool (*is_end)(char c),
+			     int argc, char *argv[])
+{
+	const char *in, *p;
+	char *expansion, *out;
+	size_t in_len, out_len;
+
+	out = xmalloc(1);
+	*out = 0;
+	out_len = 1;
+
+	p = in = *str;
+
+	while (1) {
+		if (*p == '$') {
+			in_len = p - in;
+			p++;
+			expansion = expand_dollar_with_args(&p, argc, argv);
+			out_len += in_len + strlen(expansion);
+			out = xrealloc(out, out_len);
+			strncat(out, in, in_len);
+			strcat(out, expansion);
+			free(expansion);
+			in = p;
+			continue;
+		}
+
+		if (is_end(*p))
+			break;
+
+		p++;
+	}
+
+	in_len = p - in;
+	out_len += in_len;
+	out = xrealloc(out, out_len);
+	strncat(out, in, in_len);
+
+	/* Advance 'str' to the end character */
+	*str = p;
+
+	return out;
+}
+
+static bool is_end_of_str(char c)
+{
+	return !c;
+}
+
+/*
+ * Expand variables and functions in the given string.  Undefined variables
+ * expand to an empty string.
+ * The returned string must be freed when done.
+ */
+static char *expand_string_with_args(const char *in, int argc, char *argv[])
+{
+	return __expand_string(&in, is_end_of_str, argc, argv);
+}
+
+static char *expand_string(const char *in)
+{
+	return expand_string_with_args(in, 0, NULL);
+}
+
+static bool is_end_of_token(char c)
+{
+	return !(isalnum(c) || c == '_' || c == '-');
+}
+
+/*
+ * Expand variables in a token.  The parsing stops when a token separater
+ * (in most cases, it is a whitespace) is encountered.  'str' is updated to
+ * point to the next character.
+ *
+ * The returned string must be freed when done.
+ */
+char *expand_one_token(const char **str)
+{
+	return __expand_string(str, is_end_of_token, 0, NULL);
+}