From: Vasily Averin <vvs@openvz.org>
To: Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>
Cc: kernel@openvz.org, linux-kernel@vger.kernel.org,
Konstantin Khorenko <khorenko@virtuozzo.com>,
steve.sipes@comandsolutions.com
Subject: [PATCH] x86/fault: ignore RSVD flag in error code if P flag is 0
Date: Thu, 30 Jun 2022 08:58:36 +0300 [thread overview]
Message-ID: <85bd8614-9a55-3113-e5a8-b7e73f636135@openvz.org> (raw)
In-Reply-To: <9bc8de5f-fd80-57fe-0169-0ec942638299@openvz.org>
Some older Intel CPUs have errata:
"Not-Present Page Faults May Set the RSVD Flag in the Error Code
Problem:
An attempt to access a page that is not marked present causes a page
fault. Such a page fault delivers an error code in which both the
P flag (bit 0) and the RSVD flag (bit 3) are 0. Due to this erratum,
not-present page faults may deliver an error code in which the P flag
is 0 but the RSVD flag is 1.
Implication:
Software may erroneously infer that a page fault was due to a
reserved-bit violation when it was actually due to an attempt
to access a not-present page.
Workaround: Page-fault handlers should ignore the RSVD flag in the error
code if the P flag is 0."
This issues was observed on several nodes crashed with messages
httpd: Corrupted page table at address 7f62d5b48e68
PGD 80000002e92bf067 PUD 1c99c5067 PMD 195015067 PTE 7fffffffb78b680
Bad pagetable: 000c [#1] SMP
Let's follow the recommendation and will ignore the RSVD flag in the
error code if the P flag is 0
Link: https://lore.kernel.org/all/aae9c7c6-989c-0261-470a-252537493b53@openvz.org
Signed-off-by: Vasily Averin <vvs@openvz.org>
---
arch/x86/mm/fault.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index fe10c6d76bac..ffc6d6bd2a22 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1481,6 +1481,15 @@ handle_page_fault(struct pt_regs *regs, unsigned long error_code,
if (unlikely(kmmio_fault(regs, address)))
return;
+ /*
+ * Some older Intel CPUs have errata
+ * "Not-Present Page Faults May Set the RSVD Flag in the Error Code"
+ * It is recommended to ignore the RSVD flag (bit 3) in the error code
+ * if the P flag (bit 0) is 0.
+ */
+ if (unlikely((error_code & X86_PF_RSVD) && !(error_code & X86_PF_PROT)))
+ error_code &= ~X86_PF_RSVD;
+
/* Was the fault on kernel-controlled part of the address space? */
if (unlikely(fault_in_kernel_space(address))) {
do_kern_addr_fault(regs, error_code, address);
--
2.36.1
next prev parent reply other threads:[~2022-06-30 5:58 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-20 5:29 "Bad pagetable: 000c" crashes and errata "Not-Present Page Faults May Set the RSVD Flag in the Error Code" Vasily Averin
2022-06-20 7:18 ` Dave Hansen
2022-06-20 8:00 ` Vasily Averin
2022-06-30 5:58 ` Vasily Averin [this message]
2022-06-30 14:22 ` [PATCH] x86/fault: ignore RSVD flag in error code if P flag is 0 Dave Hansen
2022-06-30 23:58 ` [PATCH v2] " Vasily Averin
2022-07-01 0:42 ` [PATCH] " H. Peter Anvin
2022-07-01 4:56 ` Vasily Averin
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