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From: Kees Cook <keescook@chromium.org>
To: Sami Tolvanen <samitolvanen@google.com>
Cc: x86@kernel.org, Josh Poimboeuf <jpoimboe@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Sedat Dilek <sedat.dilek@gmail.com>,
	linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org,
	clang-built-linux@googlegroups.com
Subject: Re: [PATCH v3 10/16] x86/extable: Mark handlers __cficanonical
Date: Tue, 14 Sep 2021 12:37:40 -0700	[thread overview]
Message-ID: <202109141235.BE65491A4@keescook> (raw)
In-Reply-To: <20210914191045.2234020-11-samitolvanen@google.com>

On Tue, Sep 14, 2021 at 12:10:39PM -0700, Sami Tolvanen wrote:
> 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@google.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,

Double __visible here, but with that fixed:

Reviewed-by: Kees Cook <keescook@chromium.org>

I would note that given Linus's recent comments on attribute locations,
it does seem that __cficanonical is more a function behavior attribute
than a storage class... I'm not really sure:
https://lore.kernel.org/mm-commits/CAHk-=wiOCLRny5aifWNhr621kYrJwhfURsa0vFPeUEm8mF0ufg@mail.gmail.com

-Kees

>  				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
> 

-- 
Kees Cook

  reply	other threads:[~2021-09-14 19:37 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-14 19:10 [PATCH v3 00/16] x86: Add support for Clang CFI Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 01/16] objtool: Add CONFIG_CFI_CLANG support Sami Tolvanen
2021-09-14 19:29   ` Nick Desaulniers
2021-09-14 21:01     ` Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 02/16] objtool: Add ASM_STACK_FRAME_NON_STANDARD Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 03/16] linkage: Add DECLARE_ASM_FUNC_SYMBOL Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 04/16] cfi: Add DEFINE_CFI_IMMEDIATE_RETURN_STUB Sami Tolvanen
2021-09-14 19:36   ` Nick Desaulniers
2021-09-14 20:32     ` Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 05/16] tracepoint: Exclude tp_stub_func from CFI checking Sami Tolvanen
2021-09-14 19:39   ` Nick Desaulniers
2021-09-14 19:10 ` [PATCH v3 06/16] ftrace: Use an opaque type for functions not callable from C Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 07/16] lkdtm: Disable UNSET_SMEP with CFI Sami Tolvanen
2021-09-14 19:30   ` Kees Cook
2021-09-14 19:10 ` [PATCH v3 08/16] lkdtm: Use an opaque type for lkdtm_rodata_do_nothing Sami Tolvanen
2021-09-14 19:32   ` Kees Cook
2021-09-14 19:10 ` [PATCH v3 09/16] x86: Use an opaque type for functions not callable from C Sami Tolvanen
2021-09-14 19:33   ` Kees Cook
2021-09-14 19:10 ` [PATCH v3 10/16] x86/extable: Mark handlers __cficanonical Sami Tolvanen
2021-09-14 19:37   ` Kees Cook [this message]
2021-09-14 20:38     ` Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 11/16] x86/purgatory: Disable CFI Sami Tolvanen
2021-09-14 20:02   ` Nick Desaulniers
2021-09-14 20:30     ` Sami Tolvanen
2021-09-14 22:31       ` Nick Desaulniers
2021-09-15  6:24         ` Kees Cook
2021-09-14 19:10 ` [PATCH v3 12/16] x86, relocs: Ignore __typeid__ relocations Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 13/16] x86, module: " Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 14/16] x86, cpu: Use LTO for cpu.c with CFI Sami Tolvanen
2021-09-14 19:44   ` Kees Cook
2021-09-14 19:46   ` Nick Desaulniers
2021-09-14 19:10 ` [PATCH v3 15/16] x86, kprobes: Fix optprobe_template_func type mismatch Sami Tolvanen
2021-09-14 19:40   ` Kees Cook
2021-09-14 19:10 ` [PATCH v3 16/16] x86, build: Allow CONFIG_CFI_CLANG to be selected Sami Tolvanen

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