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

Borislav Petkov
2017-06-09T11:02:30Z

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@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Brian Gerst <brgerst@gmail.com>
> Cc: Chen Yucong <slaoub@gmail.com>
> Cc: Chris Metcalf <cmetcalf@mellanox.com>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Fenghua Yu <fenghua.yu@intel.com>
> Cc: Huang Rui <ray.huang@amd.com>
> Cc: Jiri Slaby <jslaby@suse.cz>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ravi V. Shankar <ravi.v.shankar@intel.com>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Tony Luck <tony.luck@intel.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Liang Z. Li <liang.z.li@intel.com>
> Cc: Alexandre Julliard <julliard@winehq.org>
> Cc: Stas Sergeev <stsp@list.ru>
> Cc: x86@kernel.org
> Cc: linux-msdos@vger.kernel.org
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@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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