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authorAndy Lutomirski <luto@kernel.org>2017-03-22 14:32:29 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-05-20 14:26:59 +0200
commitd34ecdc9712c572b30a4d3173edd4b9f138f397d (patch)
tree9db07d82fa9e5fb8faed082deb5fbe77d1d4548f
parente89233f53e3d7faf6d701bdbeeffbaeee293e425 (diff)
selftests/x86/ldt_gdt_32: Work around a glibc sigaction() bug
commit 65973dd3fd31151823f4b8c289eebbb3fb7e6bc0 upstream. i386 glibc is buggy and calls the sigaction syscall incorrectly. This is asymptomatic for normal programs, but it blows up on programs that do evil things with segmentation. The ldt_gdt self-test is an example of such an evil program. This doesn't appear to be a regression -- I think I just got lucky with the uninitialized memory that glibc threw at the kernel when I wrote the test. This hackish fix manually issues sigaction(2) syscalls to undo the damage. Without the fix, ldt_gdt_32 segfaults; with the fix, it passes for me. See: https://sourceware.org/bugzilla/show_bug.cgi?id=21269 Signed-off-by: Andy Lutomirski <luto@kernel.org> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Juergen Gross <jgross@suse.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Garnier <thgarnie@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/aaab0f9f93c9af25396f01232608c163a760a668.1490218061.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--tools/testing/selftests/x86/ldt_gdt.c46
1 files changed, 46 insertions, 0 deletions
diff --git a/tools/testing/selftests/x86/ldt_gdt.c b/tools/testing/selftests/x86/ldt_gdt.c
index 31a3035cd4eb..923e59eb82c7 100644
--- a/tools/testing/selftests/x86/ldt_gdt.c
+++ b/tools/testing/selftests/x86/ldt_gdt.c
@@ -394,6 +394,51 @@ static void *threadproc(void *ctx)
}
}
+#ifdef __i386__
+
+#ifndef SA_RESTORE
+#define SA_RESTORER 0x04000000
+#endif
+
+/*
+ * The UAPI header calls this 'struct sigaction', which conflicts with
+ * glibc. Sigh.
+ */
+struct fake_ksigaction {
+ void *handler; /* the real type is nasty */
+ unsigned long sa_flags;
+ void (*sa_restorer)(void);
+ unsigned char sigset[8];
+};
+
+static void fix_sa_restorer(int sig)
+{
+ struct fake_ksigaction ksa;
+
+ if (syscall(SYS_rt_sigaction, sig, NULL, &ksa, 8) == 0) {
+ /*
+ * glibc has a nasty bug: it sometimes writes garbage to
+ * sa_restorer. This interacts quite badly with anything
+ * that fiddles with SS because it can trigger legacy
+ * stack switching. Patch it up. See:
+ *
+ * https://sourceware.org/bugzilla/show_bug.cgi?id=21269
+ */
+ if (!(ksa.sa_flags & SA_RESTORER) && ksa.sa_restorer) {
+ ksa.sa_restorer = NULL;
+ if (syscall(SYS_rt_sigaction, sig, &ksa, NULL,
+ sizeof(ksa.sigset)) != 0)
+ err(1, "rt_sigaction");
+ }
+ }
+}
+#else
+static void fix_sa_restorer(int sig)
+{
+ /* 64-bit glibc works fine. */
+}
+#endif
+
static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
int flags)
{
@@ -405,6 +450,7 @@ static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
if (sigaction(sig, &sa, 0))
err(1, "sigaction");
+ fix_sa_restorer(sig);
}
static jmp_buf jmpbuf;