From: Zhenhua Huang <quic_zhenhuah@quicinc.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Marco Elver <elver@google.com>, <catalin.marinas@arm.com>,
<will@kernel.org>, <glider@google.com>,
<akpm@linux-foundation.org>,
<linux-arm-kernel@lists.infradead.org>, <linux-mm@kvack.org>
Subject: Re: [PATCH] mm: kfence: export kfence_enabled as global variables
Date: Tue, 7 Feb 2023 20:35:52 +0800 [thread overview]
Message-ID: <1575ba20-09b7-d38b-f57d-77671d8d97cd@quicinc.com> (raw)
In-Reply-To: <Y+IsdrvDNILA59UN@FVFF77S0Q05N>
Thanks Mark!
On 2023/2/7 18:48, Mark Rutland wrote:
> On Tue, Feb 07, 2023 at 03:46:53PM +0800, Zhenhua Huang wrote:
>> Thanks Marco!
>>
>> On 2023/2/7 15:19, Marco Elver wrote:
>>> On Tue, 7 Feb 2023 at 07:15, Zhenhua Huang <quic_zhenhuah@quicinc.com> wrote:
>>>>
>>>> Export the variable to ease the judgement of whether kfence enabled
>>>> at runtime. It should be more precise than through kernel config
>>>> "CONFIG_KFENCE".
>>>>
>>>> For example We can disable kfence at runtime using bootargs
>>>> "kfence.sample_interval=0" but CONFIG_KFENCE enabled.
>>>> It was false positive.
>>>>
>>>> Signed-off-by: Zhenhua Huang <quic_zhenhuah@quicinc.com>
>>>> ---
>>>> arch/arm64/mm/pageattr.c | 3 ++-
>>>> include/linux/kfence.h | 2 ++
>>>> mm/kfence/core.c | 2 +-
>>>> 3 files changed, 5 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
>>>> index 79dd201..208d780 100644
>>>> --- a/arch/arm64/mm/pageattr.c
>>>> +++ b/arch/arm64/mm/pageattr.c
>>>> @@ -7,6 +7,7 @@
>>>> #include <linux/module.h>
>>>> #include <linux/sched.h>
>>>> #include <linux/vmalloc.h>
>>>> +#include <linux/kfence.h>
>>>>
>>>> #include <asm/cacheflush.h>
>>>> #include <asm/set_memory.h>
>>>> @@ -27,7 +28,7 @@ bool can_set_direct_map(void)
>>>> * protect/unprotect single pages.
>>>> */
>>>> return (rodata_enabled && rodata_full) || debug_pagealloc_enabled() ||
>>>> - IS_ENABLED(CONFIG_KFENCE);
>>>> + kfence_enabled;
>>>
>>> Unfortunately this won't work, because it's possible to enable KFENCE
>>> after the kernel has booted with e.g.: echo 100 >
>>> /sys/module/kfence/parameters/sample_interval
>> Yeah, got it. Thanks for catching it.
>>>
>>> What is the problem you have encountered? Is the page-granular direct
>>> map causing issues?
>> We're working on a low memory target, page-granular mapping costed more (2M
>> per 1GB) memory. Due to GKI constraints, it is not easy to disable
>> CONFIG_KFENCE. So my intention was to move the judgement to runtime
>> configurable w/ CONFIG_KFENCE on...
>>
>> Do you have any further suggestion/proposal on this? Many Thanks!
>
> Just to check, the cost is because we're mapping *all* of memory at page
> granulatrity, right? If we were to just map the KFENCE region a page
> granularity, would that be a sufficient saving?
Yes,that's expected saving which I would like to address here.
>
> We didn't do that so far because it was simpler to just map everything at page
> granularity (and that's also required by rodata_full, which I though android
> used?).
Yes, by default we're setting rodata_full. While for low-ram target, we
also can lower the security requirement. This is why I am pursuing..
BTW, rodata_full can be easily runtime configured through bootargs.
>
> If it's really important (and rodata_full isn't being used), we could try to do
> that.
>
> To do that we'd need to choose the KFENCE region *before* arm64 creates the
> fine-grain translation tables, which probable needs an arch_ hook.
It sounds a good solution. Let me also dig into this. Many Thanks!
>
> Thanks,
> Mark.
>
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
prev parent reply other threads:[~2023-02-07 12:37 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-07 6:15 [PATCH] mm: kfence: export kfence_enabled as global variables Zhenhua Huang
2023-02-07 7:19 ` Marco Elver
2023-02-07 7:46 ` Zhenhua Huang
2023-02-07 10:28 ` Alexander Potapenko
2023-02-07 10:42 ` Zhenhua Huang
2023-02-07 10:48 ` Mark Rutland
2023-02-07 12:35 ` Zhenhua Huang [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1575ba20-09b7-d38b-f57d-77671d8d97cd@quicinc.com \
--to=quic_zhenhuah@quicinc.com \
--cc=akpm@linux-foundation.org \
--cc=catalin.marinas@arm.com \
--cc=elver@google.com \
--cc=glider@google.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-mm@kvack.org \
--cc=mark.rutland@arm.com \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).