linux-kernel - [PATCH v2 37/39] x86/ibt: Finish --ibt-fix-direct on module loading

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Message-ID: <20220224151324.198359442@infradead.org>
Date:   Thu, 24 Feb 2022 15:52:15 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        jpoimboe@...hat.com, andrew.cooper3@...rix.com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com, mbenes@...e.cz, rostedt@...dmis.org,
        mhiramat@...nel.org, alexei.starovoitov@...il.com
Subject: [PATCH v2 37/39] x86/ibt: Finish --ibt-fix-direct on module loading

Since modules are not fully linked objects, per construction, the
LTO-like objtool pass cannot fix up the direct calls to external
symbols.

Have the module loader finish the job.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/kernel/module.c |   40 +++++++++++++++++++++++++++++++++++++---
 1 file changed, 37 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -24,6 +24,7 @@
 #include <asm/page.h>
 #include <asm/setup.h>
 #include <asm/unwind.h>
+#include <asm/ibt.h>
 
 #if 0
 #define DEBUGP(fmt, ...)				\
@@ -128,6 +129,33 @@ int apply_relocate(Elf32_Shdr *sechdrs,
 	return 0;
 }
 #else /*X86_64*/
+
+static inline void ibt_fix_direct(void *loc, u64 *val)
+{
+#ifdef CONFIG_X86_KERNEL_IBT
+	const void *addr = (void *)(4 + *val);
+	union text_poke_insn text;
+	u32 insn;
+
+	if (get_kernel_nofault(insn, addr))
+		return;
+
+	if (!is_endbr(insn))
+		return;
+
+	/* validate jmp.d32/call @ loc */
+	if (WARN_ONCE(get_kernel_nofault(text, loc-1) ||
+		      (text.opcode != CALL_INSN_OPCODE &&
+		       text.opcode != JMP32_INSN_OPCODE),
+		      "Unexpected code at: %pS\n", loc))
+		return;
+
+	DEBUGP("ibt_fix_direct: %pS\n", addr);
+
+	*val += 4;
+#endif
+}
+
 static int __apply_relocate_add(Elf64_Shdr *sechdrs,
 		   const char *strtab,
 		   unsigned int symindex,
@@ -139,6 +167,7 @@ static int __apply_relocate_add(Elf64_Sh
 	Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
 	Elf64_Sym *sym;
 	void *loc;
+	int type;
 	u64 val;
 
 	DEBUGP("Applying relocate section %u to %u\n",
@@ -153,13 +182,14 @@ static int __apply_relocate_add(Elf64_Sh
 		sym = (Elf64_Sym *)sechdrs[symindex].sh_addr
 			+ ELF64_R_SYM(rel[i].r_info);
 
+		type = ELF64_R_TYPE(rel[i].r_info);
+
 		DEBUGP("type %d st_value %Lx r_addend %Lx loc %Lx\n",
-		       (int)ELF64_R_TYPE(rel[i].r_info),
-		       sym->st_value, rel[i].r_addend, (u64)loc);
+		       type, sym->st_value, rel[i].r_addend, (u64)loc);
 
 		val = sym->st_value + rel[i].r_addend;
 
-		switch (ELF64_R_TYPE(rel[i].r_info)) {
+		switch (type) {
 		case R_X86_64_NONE:
 			break;
 		case R_X86_64_64:
@@ -185,6 +215,10 @@ static int __apply_relocate_add(Elf64_Sh
 		case R_X86_64_PLT32:
 			if (*(u32 *)loc != 0)
 				goto invalid_relocation;
+
+			if (type == R_X86_64_PLT32)
+				ibt_fix_direct(loc, &val);
+
 			val -= (u64)loc;
 			write(loc, &val, 4);
 #if 0