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 <luto@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/881de09e786ab93ce56ee4a2437ba2c308afe7a9.1593795633.git.luto@kernel.org
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@ -49,6 +49,23 @@
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static void check_user_regs(struct pt_regs *regs)
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{
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if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) {
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/*
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* Make sure that the entry code gave us a sensible EFLAGS
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* register. Native because we want to check the actual CPU
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* state, not the interrupt state as imagined by Xen.
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*/
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unsigned long flags = native_save_fl();
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WARN_ON_ONCE(flags & (X86_EFLAGS_AC | X86_EFLAGS_DF |
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X86_EFLAGS_NT));
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/* We think we came from user mode. Make sure pt_regs agrees. */
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WARN_ON_ONCE(!user_mode(regs));
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/*
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* All entries from user mode (except #DF) should be on the
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* normal thread stack and should have user pt_regs in the
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* correct location.
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*/
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WARN_ON_ONCE(!on_thread_stack());
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WARN_ON_ONCE(regs != task_pt_regs(current));
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}
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@ -577,6 +594,7 @@ SYSCALL_DEFINE0(ni_syscall)
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bool noinstr idtentry_enter_cond_rcu(struct pt_regs *regs)
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{
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if (user_mode(regs)) {
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check_user_regs(regs);
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enter_from_user_mode();
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return false;
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}
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@ -710,6 +728,7 @@ void noinstr idtentry_exit_cond_rcu(struct pt_regs *regs, bool rcu_exit)
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*/
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void noinstr idtentry_enter_user(struct pt_regs *regs)
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{
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check_user_regs(regs);
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enter_from_user_mode();
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}
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@ -81,5 +81,16 @@ int main(void)
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printf("[RUN]\tSet NT|AC|TF and issue a syscall\n");
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do_it(X86_EFLAGS_NT | X86_EFLAGS_AC | X86_EFLAGS_TF);
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/*
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* Now try DF. This is evil and it's plausible that we will crash
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* glibc, but glibc would have to do something rather surprising
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* for this to happen.
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*/
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printf("[RUN]\tSet DF and issue a syscall\n");
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do_it(X86_EFLAGS_DF);
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printf("[RUN]\tSet TF|DF and issue a syscall\n");
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do_it(X86_EFLAGS_TF | X86_EFLAGS_DF);
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return nerrs == 0 ? 0 : 1;
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}
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