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Date:   Tue, 14 Sep 2021 12:10:39 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     x86@...nel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH v3 10/16] x86/extable: Mark handlers __cficanonical

Exception tables are populated in assembly code, but the handlers are
called in fixup_exception, which trips indirect call checking with
CONFIG_CFI_CLANG. Mark the handlers __cficanonical to allow addresses
taken in assembly to pass CFI checking.

Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 arch/x86/mm/extable.c | 64 ++++++++++++++++++++++++-------------------
 1 file changed, 36 insertions(+), 28 deletions(-)

diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index e1664e9f969c..d16912dcbb4e 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -24,16 +24,18 @@ ex_fixup_handler(const struct exception_table_entry *x)
 	return (ex_handler_t)((unsigned long)&x->handler + x->handler);
 }
 
-__visible bool ex_handler_default(const struct exception_table_entry *fixup,
-				  struct pt_regs *regs, int trapnr,
-				  unsigned long error_code,
-				  unsigned long fault_addr)
+__visible __cficanonical
+bool ex_handler_default(const struct exception_table_entry *fixup,
+			struct pt_regs *regs, int trapnr,
+			unsigned long error_code,
+			unsigned long fault_addr)
 {
 	regs->ip = ex_fixup_addr(fixup);
 	return true;
 }
 EXPORT_SYMBOL(ex_handler_default);
 
+__visible __cficanonical
 __visible bool ex_handler_fault(const struct exception_table_entry *fixup,
 				struct pt_regs *regs, int trapnr,
 				unsigned long error_code,
@@ -55,10 +57,11 @@ EXPORT_SYMBOL_GPL(ex_handler_fault);
  * of vulnerability by restoring from the initial state (essentially, zeroing
  * out all the FPU registers) if we can't restore from the task's FPU state.
  */
-__visible bool ex_handler_fprestore(const struct exception_table_entry *fixup,
-				    struct pt_regs *regs, int trapnr,
-				    unsigned long error_code,
-				    unsigned long fault_addr)
+__visible __cficanonical
+bool ex_handler_fprestore(const struct exception_table_entry *fixup,
+			  struct pt_regs *regs, int trapnr,
+			  unsigned long error_code,
+			  unsigned long fault_addr)
 {
 	regs->ip = ex_fixup_addr(fixup);
 
@@ -70,10 +73,11 @@ __visible bool ex_handler_fprestore(const struct exception_table_entry *fixup,
 }
 EXPORT_SYMBOL_GPL(ex_handler_fprestore);
 
-__visible bool ex_handler_uaccess(const struct exception_table_entry *fixup,
-				  struct pt_regs *regs, int trapnr,
-				  unsigned long error_code,
-				  unsigned long fault_addr)
+__visible __cficanonical
+bool ex_handler_uaccess(const struct exception_table_entry *fixup,
+			struct pt_regs *regs, int trapnr,
+			unsigned long error_code,
+			unsigned long fault_addr)
 {
 	WARN_ONCE(trapnr == X86_TRAP_GP, "General protection fault in user access. Non-canonical address?");
 	regs->ip = ex_fixup_addr(fixup);
@@ -81,10 +85,11 @@ __visible bool ex_handler_uaccess(const struct exception_table_entry *fixup,
 }
 EXPORT_SYMBOL(ex_handler_uaccess);
 
-__visible bool ex_handler_copy(const struct exception_table_entry *fixup,
-			       struct pt_regs *regs, int trapnr,
-			       unsigned long error_code,
-			       unsigned long fault_addr)
+__visible __cficanonical
+bool ex_handler_copy(const struct exception_table_entry *fixup,
+		     struct pt_regs *regs, int trapnr,
+		     unsigned long error_code,
+		     unsigned long fault_addr)
 {
 	WARN_ONCE(trapnr == X86_TRAP_GP, "General protection fault in user access. Non-canonical address?");
 	regs->ip = ex_fixup_addr(fixup);
@@ -93,10 +98,11 @@ __visible bool ex_handler_copy(const struct exception_table_entry *fixup,
 }
 EXPORT_SYMBOL(ex_handler_copy);
 
-__visible bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup,
-				       struct pt_regs *regs, int trapnr,
-				       unsigned long error_code,
-				       unsigned long fault_addr)
+__visible __cficanonical
+bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup,
+			     struct pt_regs *regs, int trapnr,
+			     unsigned long error_code,
+			     unsigned long fault_addr)
 {
 	if (pr_warn_once("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pS)\n",
 			 (unsigned int)regs->cx, regs->ip, (void *)regs->ip))
@@ -110,10 +116,11 @@ __visible bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup
 }
 EXPORT_SYMBOL(ex_handler_rdmsr_unsafe);
 
-__visible bool ex_handler_wrmsr_unsafe(const struct exception_table_entry *fixup,
-				       struct pt_regs *regs, int trapnr,
-				       unsigned long error_code,
-				       unsigned long fault_addr)
+__visible __cficanonical
+bool ex_handler_wrmsr_unsafe(const struct exception_table_entry *fixup,
+			     struct pt_regs *regs, int trapnr,
+			     unsigned long error_code,
+			     unsigned long fault_addr)
 {
 	if (pr_warn_once("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pS)\n",
 			 (unsigned int)regs->cx, (unsigned int)regs->dx,
@@ -126,10 +133,11 @@ __visible bool ex_handler_wrmsr_unsafe(const struct exception_table_entry *fixup
 }
 EXPORT_SYMBOL(ex_handler_wrmsr_unsafe);
 
-__visible bool ex_handler_clear_fs(const struct exception_table_entry *fixup,
-				   struct pt_regs *regs, int trapnr,
-				   unsigned long error_code,
-				   unsigned long fault_addr)
+__visible __cficanonical
+bool ex_handler_clear_fs(const struct exception_table_entry *fixup,
+			 struct pt_regs *regs, int trapnr,
+			 unsigned long error_code,
+			 unsigned long fault_addr)
 {
 	if (static_cpu_has(X86_BUG_NULL_SEG))
 		asm volatile ("mov %0, %%fs" : : "rm" (__USER_DS));
-- 
2.33.0.309.g3052b89438-goog

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