2018-01-06 17:13:39 +03:00
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From 2b0794bbebac81a539dfd405273d61a8a16531d2 Mon Sep 17 00:00:00 2001
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From: Andy Lutomirski <luto@kernel.org>
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Date: Mon, 14 Aug 2017 22:36:19 -0700
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2018-01-07 15:17:59 +03:00
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Subject: [PATCH 024/233] x86/xen/64: Fix the reported SS and CS in SYSCALL
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2018-01-06 17:13:39 +03:00
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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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When I cleaned up the Xen SYSCALL entries, I inadvertently changed
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the reported segment registers. Before my patch, regs->ss was
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__USER(32)_DS and regs->cs was __USER(32)_CS. After the patch, they
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are FLAT_USER_CS/DS(32).
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This had a couple unfortunate effects. It confused the
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opportunistic fast return logic. It also significantly increased
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the risk of triggering a nasty glibc bug:
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https://sourceware.org/bugzilla/show_bug.cgi?id=21269
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Update the Xen entry code to change it back.
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Reported-by: Brian Gerst <brgerst@gmail.com>
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Signed-off-by: Andy Lutomirski <luto@kernel.org>
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Cc: Andrew Cooper <andrew.cooper3@citrix.com>
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Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Cc: Borislav Petkov <bp@alien8.de>
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Cc: Juergen Gross <jgross@suse.com>
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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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Cc: Thomas Gleixner <tglx@linutronix.de>
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Cc: xen-devel@lists.xenproject.org
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Fixes: 8a9949bc71a7 ("x86/xen/64: Rearrange the SYSCALL entries")
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Link: http://lkml.kernel.org/r/daba8351ea2764bb30272296ab9ce08a81bd8264.1502775273.git.luto@kernel.org
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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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(cherry picked from commit fa2016a8e7d846b306e431646d250500e1da0c33)
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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 69a6ef3aeb274efe86fd74771830354f303ccc2f)
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Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
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---
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arch/x86/xen/xen-asm_64.S | 18 ++++++++++++++++++
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1 file changed, 18 insertions(+)
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diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S
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index a8a4f4c460a6..c5fee2680abc 100644
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--- a/arch/x86/xen/xen-asm_64.S
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+++ b/arch/x86/xen/xen-asm_64.S
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@@ -88,6 +88,15 @@ RELOC(xen_sysret64, 1b+1)
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ENTRY(xen_syscall_target)
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popq %rcx
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popq %r11
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+
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+ /*
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+ * Neither Xen nor the kernel really knows what the old SS and
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+ * CS were. The kernel expects __USER_DS and __USER_CS, so
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+ * report those values even though Xen will guess its own values.
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+ */
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+ movq $__USER_DS, 4*8(%rsp)
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+ movq $__USER_CS, 1*8(%rsp)
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+
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jmp entry_SYSCALL_64_after_hwframe
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ENDPROC(xen_syscall_target)
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@@ -97,6 +106,15 @@ ENDPROC(xen_syscall_target)
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ENTRY(xen_syscall32_target)
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popq %rcx
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popq %r11
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+
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+ /*
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+ * Neither Xen nor the kernel really knows what the old SS and
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+ * CS were. The kernel expects __USER32_DS and __USER32_CS, so
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+ * report those values even though Xen will guess its own values.
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+ */
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+ movq $__USER32_DS, 4*8(%rsp)
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+ movq $__USER32_CS, 1*8(%rsp)
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+
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jmp entry_SYSCALL_compat_after_hwframe
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ENDPROC(xen_syscall32_target)
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--
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2.14.2
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