If the User-Mode Instruction Prevention CPU feature is available and enabled, a general protection fault will be issued if the instructions sgdt, sldt, sidt, str or smsw are executed from user-mode context (CPL > 0). If the fault was caused by any of the instructions protected by UMIP, fixup_umip_exception() will emulate dummy results for these instructions as follows: in virtual-8086 and protected modes, sgdt, sidt and smsw are emulated; str and sldt are not emulated. No emulation is done for user-space long mode processes.
If emulation is successful, the emulated result is passed to the user space program and no SIGSEGV signal is emitted. Cc: Andy Lutomirski <[email protected]> Cc: Andrew Morton <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Brian Gerst <[email protected]> Cc: Chen Yucong <[email protected]> Cc: Chris Metcalf <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Fenghua Yu <[email protected]> Cc: Huang Rui <[email protected]> Cc: Jiri Slaby <[email protected]> Cc: Jonathan Corbet <[email protected]> Cc: Michael S. Tsirkin <[email protected]> Cc: Paul Gortmaker <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Ravi V. Shankar <[email protected]> Cc: Shuah Khan <[email protected]> Cc: Vlastimil Babka <[email protected]> Cc: Tony Luck <[email protected]> Cc: Paolo Bonzini <[email protected]> Cc: [email protected] Reviewed-by: Andy Lutomirski <[email protected]> Signed-off-by: Ricardo Neri <[email protected]> --- arch/x86/kernel/traps.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 9aab8b8..abf4f28 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -60,6 +60,7 @@ #include <asm/trace/mpx.h> #include <asm/mpx.h> #include <asm/vm86.h> +#include <asm/umip.h> #ifdef CONFIG_X86_64 #include <asm/x86_init.h> @@ -513,6 +514,10 @@ do_general_protection(struct pt_regs *regs, long error_code) RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); cond_local_irq_enable(regs); + if (static_cpu_has(X86_FEATURE_UMIP)) + if (user_mode(regs) && fixup_umip_exception(regs)) + return; + if (v8086_mode(regs)) { local_irq_enable(); handle_vm86_fault((struct kernel_vm86_regs *) regs, error_code); -- 2.7.4
