Merge tag 'x86-core-2023-08-30-v2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 core updates from Thomas Gleixner:

 - Prevent kprobes on compiler generated CFI checking code.

   The compiler generates an instruction sequence for indirect call
   checks. If this sequence is modified with a kprobe, then the check
   fails. So the instructions must be protected against probing.

 - A few minor cleanups for the SMP code

* tag 'x86-core-2023-08-30-v2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/kprobes: Prohibit probing on compiler generated CFI checking code
  x86/smpboot: Change smp_store_boot_cpu_info() to static
  x86/smp: Remove a non-existent function declaration
  x86/smpboot: Remove a stray comment about CPU hotplug

1 files changed, 34 insertions, 0 deletions

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index f7f6042eb7e6..e8babebad7b8 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -45,6 +45,7 @@
 #include <linux/vmalloc.h>
 #include <linux/pgtable.h>
 #include <linux/set_memory.h>
+#include <linux/cfi.h>
 
 #include <asm/text-patching.h>
 #include <asm/cacheflush.h>
@@ -293,7 +294,40 @@ static int can_probe(unsigned long paddr)
 #endif
 		addr += insn.length;
 	}
+	if (IS_ENABLED(CONFIG_CFI_CLANG)) {
+		/*
+		 * The compiler generates the following instruction sequence
+		 * for indirect call checks and cfi.c decodes this;
+		 *
+		 *   movl    -<id>, %r10d       ; 6 bytes
+		 *   addl    -4(%reg), %r10d    ; 4 bytes
+		 *   je      .Ltmp1             ; 2 bytes
+		 *   ud2                        ; <- regs->ip
+		 *   .Ltmp1:
+		 *
+		 * Also, these movl and addl are used for showing expected
+		 * type. So those must not be touched.
+		 */
+		__addr = recover_probed_instruction(buf, addr);
+		if (!__addr)
+			return 0;
+
+		if (insn_decode_kernel(&insn, (void *)__addr) < 0)
+			return 0;
+
+		if (insn.opcode.value == 0xBA)
+			offset = 12;
+		else if (insn.opcode.value == 0x3)
+			offset = 6;
+		else
+			goto out;
+
+		/* This movl/addl is used for decoding CFI. */
+		if (is_cfi_trap(addr + offset))
+			return 0;
+	}
 
+out:
 	return (addr == paddr);
 }