* [PATCH] x86: be more helpful with SMEP faults @ 2014-06-10 19:08 Jiri Kosina 2014-06-10 20:18 ` Borislav Petkov 0 siblings, 1 reply; 5+ messages in thread From: Jiri Kosina @ 2014-06-10 19:08 UTC (permalink / raw) To: Thomas Gleixner, Ingo Molnar, H. Peter Anvin Cc: x86, linux-kernel, bpetkov, jroedel 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) && + (read_cr4() & X86_CR4_SMEP)) + printk(smep_warning, from_kuid(&init_user_ns, current_uid())); } printk(KERN_ALERT "BUG: unable to handle kernel "); -- Jiri Kosina SUSE Labs ^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] x86: be more helpful with SMEP faults 2014-06-10 19:08 [PATCH] x86: be more helpful with SMEP faults Jiri Kosina @ 2014-06-10 20:18 ` Borislav Petkov 2014-06-10 20:24 ` H. Peter Anvin 0 siblings, 1 reply; 5+ messages in thread From: Borislav Petkov @ 2014-06-10 20:18 UTC (permalink / raw) To: Jiri Kosina Cc: Thomas Gleixner, Ingo Molnar, H. Peter Anvin, x86, linux-kernel, jroedel 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. -- ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] x86: be more helpful with SMEP faults 2014-06-10 20:18 ` Borislav Petkov @ 2014-06-10 20:24 ` H. Peter Anvin 2014-06-10 20:49 ` Jiri Kosina 0 siblings, 1 reply; 5+ messages in thread From: H. Peter Anvin @ 2014-06-10 20:24 UTC (permalink / raw) To: Borislav Petkov, Jiri Kosina Cc: Thomas Gleixner, Ingo Molnar, x86, linux-kernel, jroedel On 06/10/2014 01:18 PM, Borislav Petkov wrote: >> 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? > Yes. Also, the Linux kernel will set or clear X86_FEATURE_SMEP to match, so the two are redundant. -hpa ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] x86: be more helpful with SMEP faults 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 0 siblings, 1 reply; 5+ messages in thread From: Jiri Kosina @ 2014-06-10 20:49 UTC (permalink / raw) To: H. Peter Anvin Cc: Borislav Petkov, Thomas Gleixner, Ingo Molnar, x86, linux-kernel, jroedel On Tue, 10 Jun 2014, H. Peter Anvin wrote: > >> @@ -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? > > Yes. Also, the Linux kernel will set or clear X86_FEATURE_SMEP to > match, so the two are redundant. From: Jiri Kosina <jkosina@suse.cz> Subject: [PATCH v2] x86: be more helpful with SMEP faults If pagefault triggers 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. Signed-off-by: Jiri Kosina <jkosina@suse.cz> --- arch/x86/mm/fault.c | 6 ++++++ 1 file changed, 6 insertions(+) - v1 -> v2: removed redundant X86_FEATURE_SMEP check diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 8e57229..6f6b0e8 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 +596,10 @@ 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) && + (read_cr4() & X86_CR4_SMEP)) + printk(smep_warning, from_kuid(&init_user_ns, current_uid())); } printk(KERN_ALERT "BUG: unable to handle kernel "); -- Jiri Kosina SUSE Labs ^ permalink raw reply related [flat|nested] 5+ messages in thread
* [tip:x86/mm] x86/smep: Be more informative when signalling an SMEP fault 2014-06-10 20:49 ` Jiri Kosina @ 2014-06-12 0:58 ` tip-bot for Jiri Kosina 0 siblings, 0 replies; 5+ messages in thread From: tip-bot for Jiri Kosina @ 2014-06-12 0:58 UTC (permalink / raw) To: linux-tip-commits; +Cc: linux-kernel, hpa, mingo, jkosina, tglx, hpa Commit-ID: eff50c347fcc8feeb8c1723c23c89aba67c60263 Gitweb: http://git.kernel.org/tip/eff50c347fcc8feeb8c1723c23c89aba67c60263 Author: Jiri Kosina <jkosina@suse.cz> AuthorDate: Tue, 10 Jun 2014 22:49:31 +0200 Committer: H. Peter Anvin <hpa@linux.intel.com> CommitDate: Wed, 11 Jun 2014 17:55:30 -0700 x86/smep: Be more informative when signalling an SMEP fault If pagefault triggers 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. Signed-off-by: Jiri Kosina <jkosina@suse.cz> Link: http://lkml.kernel.org/r/alpine.LNX.2.00.1406102248490.1321@pobox.suse.cz Signed-off-by: H. Peter Anvin <hpa@linux.intel.com> --- arch/x86/mm/fault.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 858b47b..9de4cdb 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -575,6 +575,8 @@ 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, @@ -595,6 +597,10 @@ 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) && + (read_cr4() & X86_CR4_SMEP)) + printk(smep_warning, from_kuid(&init_user_ns, current_uid())); } printk(KERN_ALERT "BUG: unable to handle kernel "); ^ permalink raw reply related [flat|nested] 5+ messages in thread
end of thread, other threads:[~2014-06-12 0:58 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2014-06-10 19:08 [PATCH] x86: be more helpful with SMEP faults Jiri Kosina 2014-06-10 20:18 ` Borislav Petkov 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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