[PATCH v7 22/26] x86/umip: Force a page fault when unable to copy emulated result to user

[Borislav Petkov]

On Fri, May 05, 2017 at 11:17:20AM -0700, Ricardo Neri wrote:
> fixup_umip_exception() will be called from do_general_protection. If the
								  ^
								  |
Please end function names with parentheses.		       ---+

> former returns false, the latter will issue a SIGSEGV with SEND_SIG_PRIV.
> However, when emulation is successful but the emulated result cannot be
> copied to user space memory, it is more accurate to issue a SIGSEGV with
> SEGV_MAPERR with the offending address.
> A new function is inspired in

That reads funny.

> force_sig_info_fault is introduced to model the page fault.
> 
> Cc: Andy Lutomirski <luto at kernel.org>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: H. Peter Anvin <hpa at zytor.com>
> Cc: Borislav Petkov <bp at suse.de>
> Cc: Brian Gerst <brgerst at gmail.com>
> Cc: Chen Yucong <slaoub at gmail.com>
> Cc: Chris Metcalf <cmetcalf at mellanox.com>
> Cc: Dave Hansen <dave.hansen at linux.intel.com>
> Cc: Fenghua Yu <fenghua.yu at intel.com>
> Cc: Huang Rui <ray.huang at amd.com>
> Cc: Jiri Slaby <jslaby at suse.cz>
> Cc: Jonathan Corbet <corbet at lwn.net>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Cc: Paul Gortmaker <paul.gortmaker at windriver.com>
> Cc: Peter Zijlstra <peterz at infradead.org>
> Cc: Ravi V. Shankar <ravi.v.shankar at intel.com>
> Cc: Shuah Khan <shuah at kernel.org>
> Cc: Vlastimil Babka <vbabka at suse.cz>
> Cc: Tony Luck <tony.luck at intel.com>
> Cc: Paolo Bonzini <pbonzini at redhat.com>
> Cc: Liang Z. Li <liang.z.li at intel.com>
> Cc: Alexandre Julliard <julliard at winehq.org>
> Cc: Stas Sergeev <stsp at list.ru>
> Cc: x86 at kernel.org
> Cc: linux-msdos at vger.kernel.org
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon at linux.intel.com>
> ---
>  arch/x86/kernel/umip.c | 45 +++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 43 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
> index c7c5795..ff7366a 100644
> --- a/arch/x86/kernel/umip.c
> +++ b/arch/x86/kernel/umip.c
> @@ -148,6 +148,41 @@ static int __emulate_umip_insn(struct insn *insn, enum umip_insn umip_inst,
>  }
>  
>  /**
> + * __force_sig_info_umip_fault() - Force a SIGSEGV with SEGV_MAPERR
> + * @address:	Address that caused the signal
> + * @regs:	Register set containing the instruction pointer
> + *
> + * Force a SIGSEGV signal with SEGV_MAPERR as the error code. This function is
> + * intended to be used to provide a segmentation fault when the result of the
> + * UMIP emulation could not be copied to the user space memory.
> + *
> + * Return: none
> + */
> +static void __force_sig_info_umip_fault(void __user *address,
> +					struct pt_regs *regs)
> +{
> +	siginfo_t info;
> +	struct task_struct *tsk = current;
> +
> +	if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV)) {

Save an indentation level:

	if (!(show_unhandled_signals && unhandled_signal(tsk, SIGSEGV)))
		return;

	printk...



> +		printk_ratelimited("%s[%d] umip emulation segfault ip:%lx sp:%lx error:%x in %lx\n",
> +				   tsk->comm, task_pid_nr(tsk), regs->ip,
> +				   regs->sp, X86_PF_USER | X86_PF_WRITE,
> +				   regs->ip);
> +	}
> +
> +	tsk->thread.cr2		= (unsigned long)address;
> +	tsk->thread.error_code	= X86_PF_USER | X86_PF_WRITE;
> +	tsk->thread.trap_nr	= X86_TRAP_PF;
> +
> +	info.si_signo	= SIGSEGV;
> +	info.si_errno	= 0;
> +	info.si_code	= SEGV_MAPERR;
> +	info.si_addr	= address;
> +	force_sig_info(SIGSEGV, &info, tsk);
> +}
> +
> +/**
>   * fixup_umip_exception() - Fixup #GP faults caused by UMIP
>   * @regs:	Registers as saved when entering the #GP trap
>   *
> @@ -235,8 +270,14 @@ bool fixup_umip_exception(struct pt_regs *regs)
>  		if ((unsigned long)uaddr == -1L)
>  			return false;
>  		nr_copied = copy_to_user(uaddr, dummy_data, dummy_data_size);
> -		if (nr_copied  > 0)
> -			return false;
> +		if (nr_copied  > 0) {
> +			/*
> +			 * If copy fails, send a signal and tell caller that
> +			 * fault was fixed up

Pls end sentences in the comments with a fullstop.

> +			 */
> +			__force_sig_info_umip_fault(uaddr, regs);
> +			return true;
> +		}
>  	}
>  
>  	/* increase IP to let the program keep going */
> -- 
> 2.9.3
> 

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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