109 lines
3.7 KiB
Diff
109 lines
3.7 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Andy Lutomirski <luto@kernel.org>
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Date: Sun, 10 Dec 2017 22:47:19 -0800
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Subject: [PATCH] x86/vsyscall/64: Explicitly set _PAGE_USER in the pagetable
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hierarchy
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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CVE-2017-5754
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The kernel is very erratic as to which pagetables have _PAGE_USER set. The
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vsyscall page gets lucky: it seems that all of the relevant pagetables are
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among the apparently arbitrary ones that set _PAGE_USER. Rather than
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relying on chance, just explicitly set _PAGE_USER.
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This will let us clean up pagetable setup to stop setting _PAGE_USER. The
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added code can also be reused by pagetable isolation to manage the
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_PAGE_USER bit in the usermode tables.
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[ tglx: Folded paravirt fix from Juergen Gross ]
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Signed-off-by: Andy Lutomirski <luto@kernel.org>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Cc: Borislav Petkov <bp@alien8.de>
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Cc: Brian Gerst <brgerst@gmail.com>
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Cc: Dave Hansen <dave.hansen@linux.intel.com>
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Cc: David Laight <David.Laight@aculab.com>
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Cc: H. Peter Anvin <hpa@zytor.com>
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Cc: Josh Poimboeuf <jpoimboe@redhat.com>
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Cc: Juergen Gross <jgross@suse.com>
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Cc: Kees Cook <keescook@chromium.org>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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(cherry picked from commit 49275fef986abfb8b476e4708aaecc07e7d3e087)
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Signed-off-by: Andy Whitcroft <apw@canonical.com>
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Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
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(cherry picked from commit 445742d3632efea229c0b974f91e56a19cf31996)
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Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
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---
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arch/x86/entry/vsyscall/vsyscall_64.c | 34 +++++++++++++++++++++++++++++++++-
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1 file changed, 33 insertions(+), 1 deletion(-)
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diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
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index ce1d7534fa53..91f3133cf5f1 100644
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--- a/arch/x86/entry/vsyscall/vsyscall_64.c
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+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
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@@ -36,6 +36,7 @@
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#include <asm/unistd.h>
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#include <asm/fixmap.h>
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#include <asm/traps.h>
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+#include <asm/paravirt.h>
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#define CREATE_TRACE_POINTS
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#include "vsyscall_trace.h"
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@@ -328,16 +329,47 @@ int in_gate_area_no_mm(unsigned long addr)
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return vsyscall_mode != NONE && (addr & PAGE_MASK) == VSYSCALL_ADDR;
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}
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+/*
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+ * The VSYSCALL page is the only user-accessible page in the kernel address
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+ * range. Normally, the kernel page tables can have _PAGE_USER clear, but
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+ * the tables covering VSYSCALL_ADDR need _PAGE_USER set if vsyscalls
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+ * are enabled.
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+ *
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+ * Some day we may create a "minimal" vsyscall mode in which we emulate
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+ * vsyscalls but leave the page not present. If so, we skip calling
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+ * this.
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+ */
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+static void __init set_vsyscall_pgtable_user_bits(void)
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+{
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+ pgd_t *pgd;
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+ p4d_t *p4d;
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+ pud_t *pud;
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+ pmd_t *pmd;
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+
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+ pgd = pgd_offset_k(VSYSCALL_ADDR);
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+ set_pgd(pgd, __pgd(pgd_val(*pgd) | _PAGE_USER));
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+ p4d = p4d_offset(pgd, VSYSCALL_ADDR);
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+#if CONFIG_PGTABLE_LEVELS >= 5
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+ p4d->p4d |= _PAGE_USER;
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+#endif
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+ pud = pud_offset(p4d, VSYSCALL_ADDR);
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+ set_pud(pud, __pud(pud_val(*pud) | _PAGE_USER));
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+ pmd = pmd_offset(pud, VSYSCALL_ADDR);
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+ set_pmd(pmd, __pmd(pmd_val(*pmd) | _PAGE_USER));
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+}
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+
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void __init map_vsyscall(void)
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{
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extern char __vsyscall_page;
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unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
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- if (vsyscall_mode != NONE)
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+ if (vsyscall_mode != NONE) {
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__set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall,
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vsyscall_mode == NATIVE
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? PAGE_KERNEL_VSYSCALL
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: PAGE_KERNEL_VVAR);
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+ set_vsyscall_pgtable_user_bits();
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+ }
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BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) !=
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(unsigned long)VSYSCALL_ADDR);
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--
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2.14.2
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