From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: x86@kernel.org, linux-hyperv@vger.kernel.org,
linux-kernel@vger.kernel.org,
"K. Y. Srinivasan" <kys@microsoft.com>,
Stephen Hemminger <stephen@networkplumber.org>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: hv_hypercall_pg page permissios
Date: Tue, 07 Apr 2020 09:28:01 +0200 [thread overview]
Message-ID: <87v9mblpq6.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20200407065500.GA28490@lst.de>
Christoph Hellwig <hch@lst.de> writes:
> Hi all,
>
> The x86 Hyper-V hypercall page (hv_hypercall_pg) is the only allocation
> in the kernel using __vmalloc with exectutable persmissions, and the
> only user of PAGE_KERNEL_RX. Is there any good reason it needs to
> be readable? Otherwise we could use vmalloc_exec and kill off
> PAGE_KERNEL_RX. Note that before 372b1e91343e6 ("drivers: hv: Turn off
> write permission on the hypercall page") it was even mapped writable..
[There is nothing secret in the hypercall page, by reading it you can
figure out if you're running on Intel or AMD (VMCALL/VMMCALL) but it's
likely not the only possible way :-)]
I see no reason for hv_hypercall_pg to remain readable. I just
smoke-tested
diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 7581cab74acb..17845db67fe2 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -382,7 +382,7 @@ void __init hyperv_init(void)
guest_id = generate_guest_id(0, LINUX_VERSION_CODE, 0);
wrmsrl(HV_X64_MSR_GUEST_OS_ID, guest_id);
- hv_hypercall_pg = __vmalloc(PAGE_SIZE, GFP_KERNEL, PAGE_KERNEL_RX);
+ hv_hypercall_pg = vmalloc_exec(PAGE_SIZE);
if (hv_hypercall_pg == NULL) {
wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
goto remove_cpuhp_state;
on a Hyper-V 2016 guest and nothing broke, feel free to go ahead and
kill PAGE_KERNEL_RX.
--
Vitaly
next prev parent reply other threads:[~2020-04-07 7:28 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 [this message]
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
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
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