From: Borislav Petkov <bp@suse.de>
To: Jiri Kosina <jkosina@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, linux-kernel@vger.kernel.org, jroedel@suse.de
Subject: Re: [PATCH] x86: be more helpful with SMEP faults
Date: Tue, 10 Jun 2014 22:18:23 +0200 [thread overview]
Message-ID: <20140610201823.GA29302@pd.tnic> (raw)
In-Reply-To: <alpine.LNX.2.00.1406102102030.1321@pobox.suse.cz>
On Tue, Jun 10, 2014 at 09:08:21PM +0200, Jiri Kosina wrote:
> If pagefault happens due to SMEP triggering, it can't be really easily
> distinguished from any other oops-causing pagefault, which might lead to
> quite some confusion when trying to understand the reason for the oops.
>
> Print an explanatory message in case the fault happened during instruction
> fetch for _PAGE_USER page which is present and executable on SMEP-enabled
> CPUs.
>
> This is consistent with what we are doing for NX already; in addition to
> immediately seeing from the oops what might be happening, it can even
> easily give a good indication to sysadmins who are carefully monitoring
> their kernel logs that someone might be trying to pwn them.
>
> Tested-by: Libor Pechacek <lpechacek@suse.cz>
> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
> ---
> arch/x86/mm/fault.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 8e57229..2466ced 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -574,6 +574,8 @@ static int is_f00f_bug(struct pt_regs *regs, unsigned long address)
>
> static const char nx_warning[] = KERN_CRIT
> "kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n";
> +static const char smep_warning[] = KERN_CRIT
> +"unable to execute userspace code (SMEP?) (uid: %d)\n";
>
> static void
> show_fault_oops(struct pt_regs *regs, unsigned long error_code,
> @@ -594,6 +596,11 @@ show_fault_oops(struct pt_regs *regs, unsigned long error_code,
>
> if (pte && pte_present(*pte) && !pte_exec(*pte))
> printk(nx_warning, from_kuid(&init_user_ns, current_uid()));
> + if (pte && pte_present(*pte) && pte_exec(*pte) &&
> + (pgd_flags(*pgd) & _PAGE_USER) &&
> + static_cpu_has(X86_FEATURE_SMEP) &&
Btw, we could probably save us this line as CR4 reserved bits should be
Must-Be-Zero and setting any of those should #GP. And I'm talking about
pre-SMEP Intel, and AMD machines.
IOW, if CR4.SMEP is set, it definitely means SMEP is present and
enabled.
hpa, that true?
> + (read_cr4() & X86_CR4_SMEP))
> + printk(smep_warning, from_kuid(&init_user_ns, current_uid()));
> }
--
Regards/Gruss,
Boris.
Sent from a fat crate under my desk. Formatting is fine.
--
next prev parent reply other threads:[~2014-06-10 20:21 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-10 19:08 [PATCH] x86: be more helpful with SMEP faults Jiri Kosina
2014-06-10 20:18 ` Borislav Petkov [this message]
2014-06-10 20:24 ` H. Peter Anvin
2014-06-10 20:49 ` Jiri Kosina
2014-06-12 0:58 ` [tip:x86/mm] x86/smep: Be more informative when signalling an SMEP fault tip-bot for Jiri Kosina
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