From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Dexuan Cui <decui@microsoft.com>, Christoph Hellwig <hch@lst.de>
Cc: Stephen Hemminger <stephen@networkplumber.org>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@amacapital.net>,
Michael Kelley <mikelley@microsoft.com>,
Ju-Hyoung Lee <juhlee@microsoft.com>,
"x86\@kernel.org" <x86@kernel.org>,
"linux-hyperv\@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
KY Srinivasan <kys@microsoft.com>
Subject: RE: hv_hypercall_pg page permissios
Date: Tue, 16 Jun 2020 11:29:33 +0200 [thread overview]
Message-ID: <87blljicjm.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <HK0P153MB0322EB3EE51073CC021D4AEABF9C0@HK0P153MB0322.APCP153.PROD.OUTLOOK.COM>
Dexuan Cui <decui@microsoft.com> writes:
>> From: linux-hyperv-owner@vger.kernel.org
>> <linux-hyperv-owner@vger.kernel.org> On Behalf Of Dexuan Cui
>> Sent: Monday, June 15, 2020 10:42 AM
>> > >
>> > > Hi hch,
>> > > The patch is merged into the mainine recently, but unluckily we noticed
>> > > a warning with CONFIG_DEBUG_WX=y
>> > >
>> > > Should we revert this patch, or figure out a way to ask the DEBUG_WX
>> > > code to ignore this page?
>> >
>> > Are you sure it is hv_hypercall_pg?
>> Yes, 100% sure. I printed the value of hv_hypercall_pg and and it matched the
>> address in the warning line " x86/mm: Found insecure W+X mapping at
>> address".
>
> I did this experiment:
> 1. export vmalloc_exec and ptdump_walk_pgd_level_checkwx.
> 2. write a test module that calls them.
> 3. It turns out that every call of vmalloc_exec() triggers such a warning.
>
> vmalloc_exec() uses PAGE_KERNEL_EXEC, which is defined as
> (__PP|__RW| 0|___A| 0|___D| 0|___G)
>
> It looks the logic in note_page() is: for_each_RW_page, if the NX bit is unset,
> then report the page as an insecure W+X mapping. IMO this explains the
> warning?
Yea, bummer.
it seems we need something like PAGE_KERNEL_READONLY_EXEC but we don't
seem to have one on x86. Hypercall page is special in a way that the
guest doesn't need to write there at all. vmalloc_exec() seems to have
only one other user on x86: module_alloc() and it has other needs. On
ARM, alloc_insn_page() does the following:
arch/arm64/kernel/probes/kprobes.c: page = vmalloc_exec(PAGE_SIZE);
arch/arm64/kernel/probes/kprobes.c- if (page) {
arch/arm64/kernel/probes/kprobes.c- set_memory_ro((unsigned long)page, 1);
arch/arm64/kernel/probes/kprobes.c- set_vm_flush_reset_perms(page);
arch/arm64/kernel/probes/kprobes.c- }
What if we do the same? (almost untested):
diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index e2137070386a..31aadfea589b 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -23,6 +23,7 @@
#include <linux/kernel.h>
#include <linux/cpuhotplug.h>
#include <linux/syscore_ops.h>
+#include <linux/set_memory.h>
#include <clocksource/hyperv_timer.h>
void *hv_hypercall_pg;
@@ -383,6 +384,8 @@ void __init hyperv_init(void)
wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
goto remove_cpuhp_state;
}
+ set_memory_ro((unsigned long)hv_hypercall_pg, 1);
+ set_vm_flush_reset_perms(hv_hypercall_pg);
rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
hypercall_msr.enable = 1;
--
Vitaly
next prev parent reply other threads:[~2020-06-16 9:29 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-07 6:55 hv_hypercall_pg page permissios Christoph Hellwig
2020-04-07 7:28 ` Vitaly Kuznetsov
2020-04-07 7:38 ` Christoph Hellwig
2020-04-07 21:01 ` Andy Lutomirski
2020-06-12 7:48 ` Dexuan Cui
2020-06-15 8:35 ` Vitaly Kuznetsov
2020-06-15 17:41 ` Dexuan Cui
2020-06-15 19:49 ` Dexuan Cui
2020-06-16 7:23 ` Christoph Hellwig
2020-06-16 10:18 ` Peter Zijlstra
2020-06-16 10:23 ` Christoph Hellwig
2020-06-16 10:24 ` Christoph Hellwig
2020-06-16 10:31 ` Peter Zijlstra
2020-06-16 10:33 ` Christoph Hellwig
2020-06-16 10:40 ` Peter Zijlstra
2020-06-16 10:42 ` Christoph Hellwig
2020-06-16 10:52 ` Christoph Hellwig
2020-06-16 11:24 ` Peter Zijlstra
2020-06-16 14:39 ` Christoph Hellwig
2020-06-16 9:29 ` Vitaly Kuznetsov [this message]
2020-06-16 9:33 ` Christoph Hellwig
2020-06-16 9:55 ` Christoph Hellwig
2020-06-16 10:08 ` Christoph Hellwig
2020-06-16 10:50 ` Vitaly Kuznetsov
2020-06-16 10:20 ` Peter Zijlstra
2020-04-07 18:10 ` Dexuan Cui
2020-04-07 20:42 ` Wei Liu
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=87blljicjm.fsf@vitty.brq.redhat.com \
--to=vkuznets@redhat.com \
--cc=decui@microsoft.com \
--cc=hch@lst.de \
--cc=juhlee@microsoft.com \
--cc=kys@microsoft.com \
--cc=linux-hyperv@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@amacapital.net \
--cc=luto@kernel.org \
--cc=mikelley@microsoft.com \
--cc=peterz@infradead.org \
--cc=stephen@networkplumber.org \
--cc=x86@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).