From: David Laight <David.Laight@ACULAB.COM>
To: 'Joerg Roedel' <joro@8bytes.org>,
"x86@kernel.org" <x86@kernel.org>,
Hyunwook Baek <baekhw@google.com>
Cc: Joerg Roedel <jroedel@suse.de>,
"stable@vger.kernel.org" <stable@vger.kernel.org>,
"hpa@zytor.com" <hpa@zytor.com>,
Andy Lutomirski <luto@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Jiri Slaby <jslaby@suse.cz>,
Dan Williams <dan.j.williams@intel.com>,
Tom Lendacky <thomas.lendacky@amd.com>,
"Juergen Gross" <jgross@suse.com>,
Kees Cook <keescook@chromium.org>,
David Rientjes <rientjes@google.com>,
Cfir Cohen <cfir@google.com>, Erdem Aktas <erdemaktas@google.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mike Stunes <mstunes@vmware.com>,
Sean Christopherson <seanjc@google.com>,
Martin Radev <martin.b.radev@gmail.com>,
Arvind Sankar <nivedita@alum.mit.edu>,
"linux-coco@lists.linux.dev" <linux-coco@lists.linux.dev>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"virtualization@lists.linux-foundation.org"
<virtualization@lists.linux-foundation.org>
Subject: RE: [PATCH 3/6] x86/sev-es: Use __put_user()/__get_user
Date: Wed, 12 May 2021 08:04:33 +0000 [thread overview]
Message-ID: <0496626f018d4d27a8034a4822170222@AcuMS.aculab.com> (raw)
In-Reply-To: <20210512075445.18935-4-joro@8bytes.org>
From: Joerg
> Sent: 12 May 2021 08:55
>
> From: Joerg Roedel <jroedel@suse.de>
>
> The put_user() and get_user() functions do checks on the address which is
> passed to them. They check whether the address is actually a user-space
> address and whether its fine to access it. They also call might_fault()
> to indicate that they could fault and possibly sleep.
>
> All of these checks are neither wanted nor required in the #VC exception
> handler, which can be invoked from almost any context and also for MMIO
> instructions from kernel space on kernel memory. All the #VC handler
> wants to know is whether a fault happened when the access was tried.
>
> This is provided by __put_user()/__get_user(), which just do the access
> no matter what.
That can't be right at all.
__put/get_user() are only valid on user addresses and will try to
fault in a missing page - so can sleep.
At best this is abused the calls.
David
> Fixes: f980f9c31a92 ("x86/sev-es: Compile early handler code into kernel image")
> Cc: stable@vger.kernel.org # v5.10+
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
> arch/x86/kernel/sev.c | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index 6530a844eb61..110b39345b40 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -342,22 +342,22 @@ static enum es_result vc_write_mem(struct es_em_ctxt *ctxt,
> switch (size) {
> case 1:
> memcpy(&d1, buf, 1);
> - if (put_user(d1, target))
> + if (__put_user(d1, target))
> goto fault;
> break;
> case 2:
> memcpy(&d2, buf, 2);
> - if (put_user(d2, target))
> + if (__put_user(d2, target))
> goto fault;
> break;
> case 4:
> memcpy(&d4, buf, 4);
> - if (put_user(d4, target))
> + if (__put_user(d4, target))
> goto fault;
> break;
> case 8:
> memcpy(&d8, buf, 8);
> - if (put_user(d8, target))
> + if (__put_user(d8, target))
> goto fault;
> break;
> default:
> @@ -396,22 +396,22 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,
>
> switch (size) {
> case 1:
> - if (get_user(d1, s))
> + if (__get_user(d1, s))
> goto fault;
> memcpy(buf, &d1, 1);
> break;
> case 2:
> - if (get_user(d2, s))
> + if (__get_user(d2, s))
> goto fault;
> memcpy(buf, &d2, 2);
> break;
> case 4:
> - if (get_user(d4, s))
> + if (__get_user(d4, s))
> goto fault;
> memcpy(buf, &d4, 4);
> break;
> case 8:
> - if (get_user(d8, s))
> + if (__get_user(d8, s))
> goto fault;
> memcpy(buf, &d8, 8);
> break;
> --
> 2.31.1
-
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next prev parent reply other threads:[~2021-05-12 8:04 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-12 7:54 [PATCH 0/6] x86/sev-es: Fixes for SEV-ES guest support Joerg Roedel
2021-05-12 7:54 ` [PATCH 1/6] x86/sev-es: Don't return NULL from sev_es_get_ghcb() Joerg Roedel
2021-05-12 7:54 ` [PATCH 2/6] x86/sev-es: Forward page-faults which happen during emulation Joerg Roedel
2021-05-12 17:31 ` Sean Christopherson
2021-05-19 13:16 ` Joerg Roedel
2021-05-12 7:54 ` [PATCH 3/6] x86/sev-es: Use __put_user()/__get_user Joerg Roedel
2021-05-12 8:04 ` David Laight [this message]
2021-05-12 8:16 ` Juergen Gross
2021-05-12 8:50 ` 'Joerg Roedel'
2021-05-12 8:58 ` Juergen Gross
2021-05-12 9:31 ` David Laight
2021-05-12 9:32 ` Joerg Roedel
2021-05-19 11:33 ` 'Joerg Roedel'
2021-05-12 8:37 ` 'Joerg Roedel'
2021-05-12 15:59 ` Dave Hansen
2021-05-12 15:57 ` Dave Hansen
2021-05-12 16:00 ` Joerg Roedel
2021-05-12 7:54 ` [PATCH 4/6] Revert "x86/sev-es: Handle string port IO to kernel memory properly" Joerg Roedel
2021-05-12 17:38 ` Sean Christopherson
2021-05-19 12:22 ` Joerg Roedel
2021-05-12 7:54 ` [PATCH 5/6] x86/sev-es: Fix error message in runtime #VC handler Joerg Roedel
2021-05-12 7:54 ` [PATCH 6/6] x86/sev-es: Leave NMI-mode before sending signals Joerg Roedel
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