From: Christophe LEROY <christophe.leroy@c-s.fr>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH 12/24] powerpc/mm: Fix reporting of kernel execute faults
Date: Fri, 30 Nov 2018 07:08:46 +0100 [thread overview]
Message-ID: <802b01de-aaf0-75b3-f337-99279afab05d@c-s.fr> (raw)
In-Reply-To: <87zhtr5d1v.fsf@linux.ibm.com>
Le 30/11/2018 à 06:50, Aneesh Kumar K.V a écrit :
> Christophe LEROY <christophe.leroy@c-s.fr> writes:
>
>> Hi Ben,
>>
>> I have an issue on the 8xx with this change
>>
>> Le 19/07/2017 à 06:49, Benjamin Herrenschmidt a écrit :
>>> We currently test for is_exec and DSISR_PROTFAULT but that doesn't
>>> make sense as this is the wrong error bit to test for an execute
>>> permission failure.
>>
>> On the 8xx, on an exec permission failure, this is the correct BIT, see
>> below extract from reference manual:
>>
>> Note that only one of bits 1, 3, and 4 will be set.
>> 1 1 if the translation of an attempted access is not in the translation
>> tables. Otherwise 0
>> 3 1 if the fetch access was to guarded memory when MSR[IR] = 1. Otherwise 0
>> 4 1 if the access is not permitted by the protection mechanism; otherwise 0.
>>
>> So on the 8xx, bit 3 is not DSISR_NOEXEC_OR_G but only DSISR_G.
>> When the PPP bits are set to No-Execute, we really get bit 4 that is
>> DSISR_PROTFAULT.
>
>
> Do you have an url for the document? I am wondering whether we can get
> Documentation/powerpc/cpu_families.txt updated with these urls?
https://www.nxp.com/docs/en/reference-manual/MPC885RM.pdf
Christophe
>
>>
>>>
>>> In fact, we had code that would return early if we had an exec
>>> fault in kernel mode so I think that was just dead code anyway.
>>>
>>> Finally the location of that test is awkward and prevents further
>>> simplifications.
>>>
>>> So instead move that test into a helper along with the existing
>>> early test for kernel exec faults and out of range accesses,
>>> and put it all in a "bad_kernel_fault()" helper. While at it
>>> test the correct error bits.
>>>
>>> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>>> ---
>>> arch/powerpc/mm/fault.c | 21 +++++++++++++++------
>>> 1 file changed, 15 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
>>> index e8d6acc888c5..aead07cf8a5b 100644
>>> --- a/arch/powerpc/mm/fault.c
>>> +++ b/arch/powerpc/mm/fault.c
>>> @@ -180,6 +180,20 @@ static int mm_fault_error(struct pt_regs *regs, unsigned long addr, int fault)
>>> return MM_FAULT_CONTINUE;
>>> }
>>>
>>> +/* Is this a bad kernel fault ? */
>>> +static bool bad_kernel_fault(bool is_exec, unsigned long error_code,
>>> + unsigned long address)
>>> +{
>>> + if (is_exec && (error_code & (DSISR_NOEXEC_OR_G | DSISR_KEYFAULT))) {
>>
>> Do you mind if we had DSISR_PROTFAULT here as well ?
>>
>> Christophe
>>
>>> + printk_ratelimited(KERN_CRIT "kernel tried to execute"
>>> + " exec-protected page (%lx) -"
>>> + "exploit attempt? (uid: %d)\n",
>>> + address, from_kuid(&init_user_ns,
>>> + current_uid()));
>>> + }
>>> + return is_exec || (address >= TASK_SIZE);
>>> +}
>>> +
>>> /*
>>> * Define the correct "is_write" bit in error_code based
>>> * on the processor family
>>> @@ -252,7 +266,7 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
>>> * The kernel should never take an execute fault nor should it
>>> * take a page fault to a kernel address.
>>> */
>>> - if (!is_user && (is_exec || (address >= TASK_SIZE)))
>>> + if (unlikely(!is_user && bad_kernel_fault(is_exec, error_code, address)))
>>> return SIGSEGV;
>>>
>>> /* We restore the interrupt state now */
>>> @@ -491,11 +505,6 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
>>> return 0;
>>> }
>>>
>>> - if (is_exec && (error_code & DSISR_PROTFAULT))
>>> - printk_ratelimited(KERN_CRIT "kernel tried to execute NX-protected"
>>> - " page (%lx) - exploit attempt? (uid: %d)\n",
>>> - address, from_kuid(&init_user_ns, current_uid()));
>>> -
>>> return SIGSEGV;
>>> }
>>> NOKPROBE_SYMBOL(__do_page_fault);
>>>
next prev parent reply other threads:[~2018-11-30 6:10 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-19 4:49 [PATCH 01/24] powerpc/mm: Move exception_enter/exit to a do_page_fault wrapper Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 02/24] powerpc/mm: Pre-filter SRR1 bits before do_page_fault() Benjamin Herrenschmidt
2017-07-22 16:43 ` LEROY Christophe
2017-07-23 1:10 ` Benjamin Herrenschmidt
2017-07-24 13:48 ` Michael Ellerman
2017-07-19 4:49 ` [PATCH 03/24] powerpc/6xx: Handle DABR match before calling do_page_fault Benjamin Herrenschmidt
2017-08-03 0:19 ` Michael Ellerman
2017-08-03 1:00 ` Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 04/24] powerpc/mm: Update definitions of DSISR bits Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 05/24] powerpc/mm: Update bits used to skip hash_page Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 06/24] powerpc/mm: Use symbolic constants for filtering SRR1 bits on ISIs Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 07/24] powerpc/mm: Move out definition of CPU specific is_write bits Benjamin Herrenschmidt
2017-07-22 16:40 ` LEROY Christophe
2017-07-23 1:06 ` Benjamin Herrenschmidt
2017-07-24 11:58 ` Michael Ellerman
2017-07-19 4:49 ` [PATCH 08/24] powerpc/mm: Move error_code checks for bad faults earlier Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 09/24] powerpc/mm: Overhaul handling of bad page faults Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 10/24] powerpc/mm: Move debugger check to notify_page_fault() Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 11/24] powerpc/mm: Simplify returns from __do_page_fault Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 12/24] powerpc/mm: Fix reporting of kernel execute faults Benjamin Herrenschmidt
2018-11-07 8:35 ` Christophe LEROY
2018-11-07 10:39 ` Benjamin Herrenschmidt
[not found] ` <87zhtr5d1v.fsf@linux.ibm.com>
2018-11-30 6:08 ` Christophe LEROY [this message]
2017-07-19 4:49 ` [PATCH 13/24] powerpc/mm: Make bad_area* helper functions Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 14/24] powerpc/mm: Rework mm_fault_error() Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 15/24] powerpc/mm: Move CMO accounting out of do_page_fault into a helper Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 16/24] powerpc/mm: Cosmetic fix to page fault accounting Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 17/24] powerpc/mm: Move the DSISR_PROTFAULT sanity check Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 18/24] powerpc/mm: Move/simplify faulthandler_disabled() and !mm check Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 19/24] powerpc/mm: Add a bunch of (un)likely annotations to do_page_fault Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 20/24] powerpc/mm: Set fault flags earlier Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 21/24] powerpc/mm: Move page fault VMA access checks to a helper Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 22/24] powerpc/mm: Don't lose "major" fault indication on retry Benjamin Herrenschmidt
2017-07-19 4:49 ` [PATCH 23/24] powerpc/mm: Cleanup check for stack expansion Benjamin Herrenschmidt
2017-07-21 16:59 ` LEROY Christophe
2017-07-24 10:47 ` Michael Ellerman
2017-07-24 17:34 ` LEROY Christophe
2017-07-25 11:19 ` Michael Ellerman
2017-07-31 11:37 ` Christophe LEROY
2017-07-19 4:49 ` [PATCH 24/24] powerpc: Remove old unused icswx based coprocessor support Benjamin Herrenschmidt
2017-08-07 10:41 ` [01/24] powerpc/mm: Move exception_enter/exit to a do_page_fault wrapper Michael Ellerman
2017-08-07 16:37 ` Christophe LEROY
2017-08-08 2:16 ` Michael Ellerman
2017-08-08 6:45 ` Christophe LEROY
2017-08-08 10:00 ` Michael Ellerman
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