[PATCH v7 07/41] x86: Move control protection handler to separate file

Rick Edgecombe
2023-02-27T22:32:31Z

Today the control protection handler is defined in traps.c and used only
for the kernel IBT feature. To reduce ifdeffery, move it to it's own file.
In future patches, functionality will be added to make this handler also
handle user shadow stack faults. So name the file cet.c.

No functional change.

Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Kees Cook <keescook@chromium.org>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>

---
v6:
- Split move to cet.c and shadow stack enhancements to fault handler to
separate files. (Kees)
---
arch/x86/kernel/Makefile | 2 ++
arch/x86/kernel/cet.c | 76 ++++++++++++++++++++++++++++++++++++++++
arch/x86/kernel/traps.c | 75 ---------------------------------------
3 files changed, 78 insertions(+), 75 deletions(-)
create mode 100644 arch/x86/kernel/cet.c

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index dd61752f4c96..92446f1dedd7 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -144,6 +144,8 @@ obj-$(CONFIG_CFI_CLANG) += cfi.o

obj-$(CONFIG_CALL_THUNKS) += callthunks.o

+obj-$(CONFIG_X86_CET) += cet.o
+
###
# 64 bit specific files
ifeq ($(CONFIG_X86_64),y)
diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c
new file mode 100644
index 000000000000..7ad22b705b64
--- /dev/null
+++ b/arch/x86/kernel/cet.c
@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/ptrace.h>
+#include <asm/bugs.h>
+#include <asm/traps.h>
+
+static __ro_after_init bool ibt_fatal = true;
+
+extern void ibt_selftest_ip(void); /* code label defined in asm below */
+
+enum cp_error_code {
+ CP_EC = (1 << 15) - 1,
+
+ CP_RET = 1,
+ CP_IRET = 2,
+ CP_ENDBR = 3,
+ CP_RSTRORSSP = 4,
+ CP_SETSSBSY = 5,
+
+ CP_ENCL = 1 << 15,
+};
+
+DEFINE_IDTENTRY_ERRORCODE(exc_control_protection)
+{
+ if (!cpu_feature_enabled(X86_FEATURE_IBT)) {
+ pr_err("Unexpected #CP\n");
+ BUG();
+ }
+
+ if (WARN_ON_ONCE(user_mode(regs) || (error_code & CP_EC) != CP_ENDBR))
+ return;
+
+ if (unlikely(regs->ip == (unsigned long)&ibt_selftest_ip)) {
+ regs->ax = 0;
+ return;
+ }
+
+ pr_err("Missing ENDBR: %pS\n", (void *)instruction_pointer(regs));
+ if (!ibt_fatal) {
+ printk(KERN_DEFAULT CUT_HERE);
+ __warn(__FILE__, __LINE__, (void *)regs->ip, TAINT_WARN, regs, NULL);
+ return;
+ }
+ BUG();
+}
+
+/* Must be noinline to ensure uniqueness of ibt_selftest_ip. */
+noinline bool ibt_selftest(void)
+{
+ unsigned long ret;
+
+ asm (" lea ibt_selftest_ip(%%rip), %%rax\n\t"
+ ANNOTATE_RETPOLINE_SAFE
+ " jmp *%%rax\n\t"
+ "ibt_selftest_ip:\n\t"
+ UNWIND_HINT_FUNC
+ ANNOTATE_NOENDBR
+ " nop\n\t"
+
+ : "=a" (ret) : : "memory");
+
+ return !ret;
+}
+
+static int __init ibt_setup(char *str)
+{
+ if (!strcmp(str, "off"))
+ setup_clear_cpu_cap(X86_FEATURE_IBT);
+
+ if (!strcmp(str, "warn"))
+ ibt_fatal = false;
+
+ return 1;
+}
+
+__setup("ibt=", ibt_setup);
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index d317dc3d06a3..cc223e60aba2 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -213,81 +213,6 @@ DEFINE_IDTENTRY(exc_overflow)
do_error_trap(regs, 0, "overflow", X86_TRAP_OF, SIGSEGV, 0, NULL);
}

-#ifdef CONFIG_X86_KERNEL_IBT
-
-static __ro_after_init bool ibt_fatal = true;
-
-extern void ibt_selftest_ip(void); /* code label defined in asm below */
-
-enum cp_error_code {
- CP_EC = (1 << 15) - 1,
-
- CP_RET = 1,
- CP_IRET = 2,
- CP_ENDBR = 3,
- CP_RSTRORSSP = 4,
- CP_SETSSBSY = 5,
-
- CP_ENCL = 1 << 15,
-};
-
-DEFINE_IDTENTRY_ERRORCODE(exc_control_protection)
-{
- if (!cpu_feature_enabled(X86_FEATURE_IBT)) {
- pr_err("Unexpected #CP\n");
- BUG();
- }
-
- if (WARN_ON_ONCE(user_mode(regs) || (error_code & CP_EC) != CP_ENDBR))
- return;
-
- if (unlikely(regs->ip == (unsigned long)&ibt_selftest_ip)) {
- regs->ax = 0;
- return;
- }
-
- pr_err("Missing ENDBR: %pS\n", (void *)instruction_pointer(regs));
- if (!ibt_fatal) {
- printk(KERN_DEFAULT CUT_HERE);
- __warn(__FILE__, __LINE__, (void *)regs->ip, TAINT_WARN, regs, NULL);
- return;
- }
- BUG();
-}
-
-/* Must be noinline to ensure uniqueness of ibt_selftest_ip. */
-noinline bool ibt_selftest(void)
-{
- unsigned long ret;
-
- asm (" lea ibt_selftest_ip(%%rip), %%rax\n\t"
- ANNOTATE_RETPOLINE_SAFE
- " jmp *%%rax\n\t"
- "ibt_selftest_ip:\n\t"
- UNWIND_HINT_FUNC
- ANNOTATE_NOENDBR
- " nop\n\t"
-
- : "=a" (ret) : : "memory");
-
- return !ret;
-}
-
-static int __init ibt_setup(char *str)
-{
- if (!strcmp(str, "off"))
- setup_clear_cpu_cap(X86_FEATURE_IBT);
-
- if (!strcmp(str, "warn"))
- ibt_fatal = false;
-
- return 1;
-}
-
-__setup("ibt=", ibt_setup);
-
-#endif /* CONFIG_X86_KERNEL_IBT */
-
#ifdef CONFIG_X86_F00F_BUG
void handle_invalid_op(struct pt_regs *regs)
#else
--
2.17.1