[kernel-hardening] Re: [PATCH RFC v6 5/6] fs/proc: Show STACKLEAK metrics in the /proc file system

[Laura Abbott <labbott@redhat.com>]

On 12/05/2017 03:33 PM, Alexander Popov wrote:
> Introduce CONFIG_STACKLEAK_METRICS providing STACKLEAK information about
> tasks via the /proc file system. In particular, /proc/<pid>/lowest_stack
> shows the current lowest_stack value and its final value from the previous
> syscall. That information can be useful for estimating the STACKLEAK
> performance impact for different workloads.
> 
> Signed-off-by: Alexander Popov <alex.popov@linux.com>
> ---
>   arch/Kconfig                     | 11 +++++++++++
>   arch/x86/entry/entry_32.S        |  4 ++++
>   arch/x86/entry/entry_64.S        |  4 ++++
>   arch/x86/include/asm/processor.h |  3 +++
>   arch/x86/kernel/asm-offsets.c    |  3 +++
>   arch/x86/kernel/process_32.c     |  3 +++
>   arch/x86/kernel/process_64.c     |  3 +++
>   fs/proc/base.c                   | 14 ++++++++++++++
>   8 files changed, 45 insertions(+)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index ba8e67b..3d8405c 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -559,6 +559,17 @@ config STACKLEAK_TRACK_MIN_SIZE
>   	  this setting, don't break the poison search in erase_kstack.
>   	  If unsure, leave the default value 100.
>   
> +config STACKLEAK_METRICS
> +	bool "Show STACKLEAK metrics in the /proc file system"
> +	depends on GCC_PLUGIN_STACKLEAK
> +	depends on PROC_FS
> +	help
> +	  If this is set, STACKLEAK metrics for every task are available in
> +	  the /proc file system. In particular, /proc/<pid>/lowest_stack
> +	  shows the current lowest_stack value and its final value from the
> +	  previous syscall. That information can be useful for estimating
> +	  the STACKLEAK performance impact for your workloads.
> +
>   config HAVE_CC_STACKPROTECTOR
>   	bool
>   	help
> diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
> index 8e4f815..2b76020 100644
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -116,6 +116,10 @@ ENTRY(erase_kstack)
>   	mov	%esp, %ecx
>   	sub	%edi, %ecx
>   
> +#ifdef CONFIG_STACKLEAK_METRICS
> +	mov	%edi, TASK_prev_lowest_stack(%ebp)
> +#endif
> +
>   	cmp	$THREAD_SIZE_asm, %ecx
>   	jb	3f
>   	ud2
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 94f659d..32ee040 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -121,6 +121,10 @@ ENTRY(erase_kstack)
>   	mov	%esp, %ecx
>   	sub	%edi, %ecx
>   
> +#ifdef CONFIG_STACKLEAK_METRICS
> +	mov	%rdi, TASK_prev_lowest_stack(%r11)
> +#endif
> +
>   	/* Check that the counter value is sane. */
>   	cmp	$THREAD_SIZE_asm, %rcx
>   	jb	3f
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index 520508d..c94fc2f 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -483,6 +483,9 @@ struct thread_struct {
>   
>   #ifdef CONFIG_GCC_PLUGIN_STACKLEAK
>   	unsigned long		lowest_stack;
> +# ifdef CONFIG_STACKLEAK_METRICS
> +	unsigned long		prev_lowest_stack;
> +# endif
>   #endif
>   
>   	unsigned int		sig_on_uaccess_err:1;
> diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
> index 692c10e..84c5a29 100644
> --- a/arch/x86/kernel/asm-offsets.c
> +++ b/arch/x86/kernel/asm-offsets.c
> @@ -43,6 +43,9 @@ void common(void) {
>   # ifdef CONFIG_X86_32
>   	OFFSET(TASK_thread_sp0, task_struct, thread.sp0);
>   # endif
> +# ifdef CONFIG_STACKLEAK_METRICS
> +	OFFSET(TASK_prev_lowest_stack, task_struct, thread.prev_lowest_stack);
> +# endif
>   #endif
>   
>   	BLANK();
> diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
> index 2bea3bf..5615b3d 100644
> --- a/arch/x86/kernel/process_32.c
> +++ b/arch/x86/kernel/process_32.c
> @@ -139,6 +139,9 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
>   #ifdef CONFIG_GCC_PLUGIN_STACKLEAK
>   	p->thread.lowest_stack = (unsigned long)task_stack_page(p) +
>   						2 * sizeof(unsigned long);
> +# ifdef CONFIG_STACKLEAK_METRICS
> +	p->thread.prev_lowest_stack = p->thread.lowest_stack;
> +# endif
>   #endif
>   
>   	if (unlikely(p->flags & PF_KTHREAD)) {
> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> index 1641463..d4a50ef 100644
> --- a/arch/x86/kernel/process_64.c
> +++ b/arch/x86/kernel/process_64.c
> @@ -285,6 +285,9 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
>   #ifdef CONFIG_GCC_PLUGIN_STACKLEAK
>   	p->thread.lowest_stack = (unsigned long)task_stack_page(p) +
>   						2 * sizeof(unsigned long);
> +# ifdef CONFIG_STACKLEAK_METRICS
> +	p->thread.prev_lowest_stack = p->thread.lowest_stack;
> +# endif
>   #endif
>   
>   	savesegment(gs, p->thread.gsindex);
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 28fa852..3569446 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2884,6 +2884,17 @@ static int proc_pid_patch_state(struct seq_file *m, struct pid_namespace *ns,
>   }
>   #endif /* CONFIG_LIVEPATCH */
>   
> +#ifdef CONFIG_STACKLEAK_METRICS
> +static int proc_lowest_stack(struct seq_file *m, struct pid_namespace *ns,
> +				struct pid *pid, struct task_struct *task)
> +{
> +	seq_printf(m, "prev_lowest_stack: %pK\nlowest_stack: %pK\n",
> +		   (void *)task->thread.prev_lowest_stack,
> +		   (void *)task->thread.lowest_stack);
> +	return 0;
> +}
> +#endif /* CONFIG_STACKLEAK_METRICS */
> +

This just prints the hashed value with the new pointer leak work.
I don't think we want to print the fully exposed value via %px so
it's not clear how valuable this proc file is now.

Thanks,
Laura

>   /*
>    * Thread groups
>    */
> @@ -2988,6 +2999,9 @@ static const struct pid_entry tgid_base_stuff[] = {
>   #ifdef CONFIG_LIVEPATCH
>   	ONE("patch_state",  S_IRUSR, proc_pid_patch_state),
>   #endif
> +#ifdef CONFIG_STACKLEAK_METRICS
> +	ONE("lowest_stack", S_IRUGO, proc_lowest_stack),
> +#endif
>   };
>   
>   static int proc_tgid_base_readdir(struct file *file, struct dir_context *ctx)
>