From: Andy Lutomirski Date: Thu, 19 Mar 2015 01:33:29 +0000 (-0700) Subject: x86/asm/entry: Add user_mode_ignore_vm86() X-Git-Tag: firefly_0821_release~176^2~2028^2~72 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=a67e7277d01ccfd39b0db5a198c2643cc19dd79c;p=firefly-linux-kernel-4.4.55.git x86/asm/entry: Add user_mode_ignore_vm86() user_mode() is dangerous and user_mode_vm() has a confusing name. Add user_mode_ignore_vm86() (equivalent to current user_mode()). We'll change the small number of legitimate users of user_mode() to user_mode_ignore_vm86(). Inspired by grsec, although this works rather differently. Signed-off-by: Andy Lutomirski Cc: Borislav Petkov Cc: Brad Spengler Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/202c56ca63823c338af8e2e54948dbe222da6343.1426728647.git.luto@kernel.org Signed-off-by: Ingo Molnar --- diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h index 83b874da2762..4a040f0078f2 100644 --- a/arch/x86/include/asm/ptrace.h +++ b/arch/x86/include/asm/ptrace.h @@ -121,6 +121,23 @@ static inline int user_mode_vm(struct pt_regs *regs) #endif } +/* + * This is the fastest way to check whether regs come from user space. + * It is unsafe if regs might come from vm86 mode, though -- in vm86 + * mode, all bits of CS and SS are completely under the user's control. + * The CPU considers vm86 mode to be CPL 3 regardless of CS and SS. + * + * Do NOT use this function unless you have already ruled out the + * possibility that regs came from vm86 mode. + * + * We check for RPL != 0 instead of RPL == 3 because we don't use rings + * 1 or 2 and this is more efficient. + */ +static inline int user_mode_ignore_vm86(struct pt_regs *regs) +{ + return (regs->cs & SEGMENT_RPL_MASK) != 0; +} + static inline int v8086_mode(struct pt_regs *regs) { #ifdef CONFIG_X86_32