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| author | Andy Lutomirski <luto@kernel.org> | 2019-05-14 13:24:39 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-05-21 18:48:55 +0200 |
| commit | f7154aa582a6a26fab8ba8b54054c610cfee10f3 (patch) | |
| tree | 98022b8b5310411f154c98d852c1ec93d852901e | |
| parent | 7227474b11fcb8e6f2e6061f261446af84a0709b (diff) | |
| download | linux-rt-f7154aa582a6a26fab8ba8b54054c610cfee10f3.tar.gz | |
x86/speculation/mds: Revert CPU buffer clear on double fault exit
commit 88640e1dcd089879530a49a8d212d1814678dfe7 upstream.
The double fault ESPFIX path doesn't return to user mode at all --
it returns back to the kernel by simulating a #GP fault.
prepare_exit_to_usermode() will run on the way out of
general_protection before running user code.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jon Masters <jcm@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Fixes: 04dcbdb80578 ("x86/speculation/mds: Clear CPU buffers on exit to user")
Link: http://lkml.kernel.org/r/ac97612445c0a44ee10374f6ea79c222fe22a5c4.1557865329.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | Documentation/x86/mds.rst | 7 | ||||
| -rw-r--r-- | arch/x86/kernel/traps.c | 8 |
2 files changed, 0 insertions, 15 deletions
diff --git a/Documentation/x86/mds.rst b/Documentation/x86/mds.rst index 534e9baa4e1d..0dc812bb9249 100644 --- a/Documentation/x86/mds.rst +++ b/Documentation/x86/mds.rst @@ -158,13 +158,6 @@ Mitigation points mitigated on the return from do_nmi() to provide almost complete coverage. - - Double fault (#DF): - - A double fault is usually fatal, but the ESPFIX workaround, which can - be triggered from user space through modify_ldt(2) is a recoverable - double fault. #DF uses the paranoid exit path, so explicit mitigation - in the double fault handler is required. - - Machine Check Exception (#MC): Another corner case is a #MC which hits between the CPU buffer clear diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index ef225fa8e928..5bbfa2f63b8c 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -62,7 +62,6 @@ #include <asm/alternative.h> #include <asm/fpu/xstate.h> #include <asm/trace/mpx.h> -#include <asm/nospec-branch.h> #include <asm/mpx.h> #include <asm/vm86.h> @@ -341,13 +340,6 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code) regs->ip = (unsigned long)general_protection; regs->sp = (unsigned long)&normal_regs->orig_ax; - /* - * This situation can be triggered by userspace via - * modify_ldt(2) and the return does not take the regular - * user space exit, so a CPU buffer clear is required when - * MDS mitigation is enabled. - */ - mds_user_clear_cpu_buffers(); return; } #endif |