This is a note to let you know that I've just added the patch titled
x86/mm, mm/hwpoison: Clear PRESENT bit for kernel 1:1 mappings of poison pages
to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-mm-mm-hwpoison-clear-present-bit-for-kernel-1-1-mappings-of-poison-pages.patch
and it can be found in the queue-4.13 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From ce0fa3e56ad20f04d8252353dcd24e924abdafca Mon Sep 17 00:00:00 2001
From: Tony Luck <tony.luck@xxxxxxxxx>
Date: Wed, 16 Aug 2017 10:18:03 -0700
Subject: x86/mm, mm/hwpoison: Clear PRESENT bit for kernel 1:1 mappings of poison pages
From: Tony Luck <tony.luck@xxxxxxxxx>
commit ce0fa3e56ad20f04d8252353dcd24e924abdafca upstream.
Speculative processor accesses may reference any memory that has a
valid page table entry. While a speculative access won't generate
a machine check, it will log the error in a machine check bank. That
could cause escalation of a subsequent error since the overflow bit
will be then set in the machine check bank status register.
Code has to be double-plus-tricky to avoid mentioning the 1:1 virtual
address of the page we want to map out otherwise we may trigger the
very problem we are trying to avoid. We use a non-canonical address
that passes through the usual Linux table walking code to get to the
same "pte".
Thanks to Dave Hansen for reviewing several iterations of this.
Also see:
http://marc.info/?l=linux-mm&m=149860136413338&w=2
Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: Elliott, Robert (Persistent Memory) <elliott@xxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Link: http://lkml.kernel.org/r/20170816171803.28342-1-tony.luck@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/page_64.h | 4 +++
arch/x86/kernel/cpu/mcheck/mce.c | 43 +++++++++++++++++++++++++++++++++++++++
include/linux/mm_inline.h | 6 +++++
mm/memory-failure.c | 2 +
4 files changed, 55 insertions(+)
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -51,6 +51,10 @@ static inline void clear_page(void *page
void copy_page(void *to, void *from);
+#ifdef CONFIG_X86_MCE
+#define arch_unmap_kpfn arch_unmap_kpfn
+#endif
+
#endif /* !__ASSEMBLY__ */
#ifdef CONFIG_X86_VSYSCALL_EMULATION
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -51,6 +51,7 @@
#include <asm/mce.h>
#include <asm/msr.h>
#include <asm/reboot.h>
+#include <asm/set_memory.h>
#include "mce-internal.h"
@@ -1051,6 +1052,48 @@ static int do_memory_failure(struct mce
return ret;
}
+#if defined(arch_unmap_kpfn) && defined(CONFIG_MEMORY_FAILURE)
+
+void arch_unmap_kpfn(unsigned long pfn)
+{
+ unsigned long decoy_addr;
+
+ /*
+ * Unmap this page from the kernel 1:1 mappings to make sure
+ * we don't log more errors because of speculative access to
+ * the page.
+ * We would like to just call:
+ * set_memory_np((unsigned long)pfn_to_kaddr(pfn), 1);
+ * but doing that would radically increase the odds of a
+ * speculative access to the posion page because we'd have
+ * the virtual address of the kernel 1:1 mapping sitting
+ * around in registers.
+ * Instead we get tricky. We create a non-canonical address
+ * that looks just like the one we want, but has bit 63 flipped.
+ * This relies on set_memory_np() not checking whether we passed
+ * a legal address.
+ */
+
+/*
+ * Build time check to see if we have a spare virtual bit. Don't want
+ * to leave this until run time because most developers don't have a
+ * system that can exercise this code path. This will only become a
+ * problem if/when we move beyond 5-level page tables.
+ *
+ * Hard code "9" here because cpp doesn't grok ilog2(PTRS_PER_PGD)
+ */
+#if PGDIR_SHIFT + 9 < 63
+ decoy_addr = (pfn << PAGE_SHIFT) + (PAGE_OFFSET ^ BIT(63));
+#else
+#error "no unused virtual bit available"
+#endif
+
+ if (set_memory_np(decoy_addr, 1))
+ pr_warn("Could not invalidate pfn=0x%lx from 1:1 map\n", pfn);
+
+}
+#endif
+
/*
* The actual machine check handler. This only handles real
* exceptions when something got corrupted coming in through int 18.
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -126,4 +126,10 @@ static __always_inline enum lru_list pag
#define lru_to_page(head) (list_entry((head)->prev, struct page, lru))
+#ifdef arch_unmap_kpfn
+extern void arch_unmap_kpfn(unsigned long pfn);
+#else
+static __always_inline void arch_unmap_kpfn(unsigned long pfn) { }
+#endif
+
#endif
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1146,6 +1146,8 @@ int memory_failure(unsigned long pfn, in
return 0;
}
+ arch_unmap_kpfn(pfn);
+
orig_head = hpage = compound_head(p);
num_poisoned_pages_inc();
Patches currently in stable-queue which might be from tony.luck@xxxxxxxxx are
queue-4.13/x86-mm-mm-hwpoison-clear-present-bit-for-kernel-1-1-mappings-of-poison-pages.patch