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| author | Andy Lutomirski <luto@kernel.org> | 2020-07-03 20:02:54 +0300 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2020-07-04 20:47:25 +0300 |
| commit | 3c73b81a9164d0c1b6379d6672d2772a9e95168e (patch) | |
| tree | c8af1056a6fdf747ff0cc9c11b4727f9ce051720 | |
| parent | db5b2c5a90a111618f071d231a8b945cf522313e (diff) | |
| download | linux-3c73b81a9164d0c1b6379d6672d2772a9e95168e.tar.xz | |
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
| -rw-r--r-- | arch/x86/entry/common.c | 19 | ||||
| -rw-r--r-- | tools/testing/selftests/x86/syscall_nt.c | 11 |
2 files changed, 30 insertions, 0 deletions
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(); } diff --git a/tools/testing/selftests/x86/syscall_nt.c b/tools/testing/selftests/x86/syscall_nt.c index 970e5e14d96d..a108b80dd082 100644 --- a/tools/testing/selftests/x86/syscall_nt.c +++ b/tools/testing/selftests/x86/syscall_nt.c @@ -81,5 +81,16 @@ int main(void) printf("[RUN]\tSet NT|AC|TF and issue a syscall\n"); do_it(X86_EFLAGS_NT | X86_EFLAGS_AC | X86_EFLAGS_TF); + /* + * Now try DF. This is evil and it's plausible that we will crash + * glibc, but glibc would have to do something rather surprising + * for this to happen. + */ + printf("[RUN]\tSet DF and issue a syscall\n"); + do_it(X86_EFLAGS_DF); + + printf("[RUN]\tSet TF|DF and issue a syscall\n"); + do_it(X86_EFLAGS_TF | X86_EFLAGS_DF); + return nerrs == 0 ? 0 : 1; } |