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There's a fair amount of code in the vsyscall page. It contains a syscall instruction (in the gettimeofday fallback) and who knows what will happen if an exploit jumps into the middle of some other code. Reduce the risk by replacing the vsyscalls with short magic incantations that cause the kernel to emulate the real vsyscalls. These incantations are useless if entered in the middle. This causes vsyscalls to be a little more expensive than real syscalls. Fortunately sensible programs don't use them. The only exception is time() which is still called by glibc through the vsyscall - but calling time() millions of times per second is not sensible. glibc has this fixed in the development tree. This patch is not perfect: the vread_tsc and vread_hpet functions are still at a fixed address. Fixing that might involve making alternative patching work in the vDSO. Signed-off-by: Andy Lutomirski <luto@mit.edu> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Jesper Juhl <jj@chaosbits.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Arjan van de Ven <arjan@infradead.org> Cc: Jan Beulich <JBeulich@novell.com> Cc: richard -rw- weinberger <richard.weinberger@gmail.com> Cc: Mikael Pettersson <mikpe@it.uu.se> Cc: Andi Kleen <andi@firstfloor.org> Cc: Brian Gerst <brgerst@gmail.com> Cc: Louis Rilling <Louis.Rilling@kerlabs.com> Cc: Valdis.Kletnieks@vt.edu Cc: pageexec@freemail.hu Link: http://lkml.kernel.org/r/e64e1b3c64858820d12c48fa739efbd1485e79d5.1307292171.git.luto@mit.edu [ Removed the CONFIG option - it's simpler to just do it unconditionally. Tidied up the code as well. ] Signed-off-by: Ingo Molnar <mingo@elte.hu>
28 lines
550 B
ArmAsm
28 lines
550 B
ArmAsm
/*
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* vsyscall_emu_64.S: Vsyscall emulation page
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*
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* Copyright (c) 2011 Andy Lutomirski
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*
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* Subject to the GNU General Public License, version 2
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*/
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#include <linux/linkage.h>
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#include <asm/irq_vectors.h>
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/* The unused parts of the page are filled with 0xcc by the linker script. */
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.section .vsyscall_0, "a"
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ENTRY(vsyscall_0)
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int $VSYSCALL_EMU_VECTOR
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END(vsyscall_0)
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.section .vsyscall_1, "a"
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ENTRY(vsyscall_1)
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int $VSYSCALL_EMU_VECTOR
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END(vsyscall_1)
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.section .vsyscall_2, "a"
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ENTRY(vsyscall_2)
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int $VSYSCALL_EMU_VECTOR
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END(vsyscall_2)
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