From 3c73b81a9164d0c1b6379d6672d2772a9e95168e Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Fri, 3 Jul 2020 10:02:54 -0700 Subject: x86/entry, selftests: Further improve user entry sanity checks Chasing down a Xen bug caused me to realize that the new entry sanity checks are still fairly weak. Add some more checks. Signed-off-by: Andy Lutomirski Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/881de09e786ab93ce56ee4a2437ba2c308afe7a9.1593795633.git.luto@kernel.org --- arch/x86/entry/common.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) (limited to 'arch/x86') diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index f392a8bcd1c3..e83b3f14897c 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -49,6 +49,23 @@ static void check_user_regs(struct pt_regs *regs) { if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) { + /* + * Make sure that the entry code gave us a sensible EFLAGS + * register. Native because we want to check the actual CPU + * state, not the interrupt state as imagined by Xen. + */ + unsigned long flags = native_save_fl(); + WARN_ON_ONCE(flags & (X86_EFLAGS_AC | X86_EFLAGS_DF | + X86_EFLAGS_NT)); + + /* We think we came from user mode. Make sure pt_regs agrees. */ + WARN_ON_ONCE(!user_mode(regs)); + + /* + * All entries from user mode (except #DF) should be on the + * normal thread stack and should have user pt_regs in the + * correct location. + */ WARN_ON_ONCE(!on_thread_stack()); WARN_ON_ONCE(regs != task_pt_regs(current)); } @@ -577,6 +594,7 @@ SYSCALL_DEFINE0(ni_syscall) bool noinstr idtentry_enter_cond_rcu(struct pt_regs *regs) { if (user_mode(regs)) { + check_user_regs(regs); enter_from_user_mode(); return false; } @@ -710,6 +728,7 @@ void noinstr idtentry_exit_cond_rcu(struct pt_regs *regs, bool rcu_exit) */ void noinstr idtentry_enter_user(struct pt_regs *regs) { + check_user_regs(regs); enter_from_user_mode(); } -- cgit v1.2.3