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[PATCH 4.4 20/56] selftests/x86/ldt_gdt_32: Work around a glibc sigaction() bug

From Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Newsgroups linux.kernel
Subject [PATCH 4.4 20/56] selftests/x86/ldt_gdt_32: Work around a glibc sigaction() bug
Date 2017-05-18 13:20 +0200
Message-ID <tIrDk-1Ek-5@gated-at.bofh.it> (permalink)
References <tIrtD-1zL-3@gated-at.bofh.it>
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4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andy Lutomirski <luto@kernel.org>

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>

---
 tools/testing/selftests/x86/ldt_gdt.c |   46 ++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

--- 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 (*h
 	if (sigaction(sig, &sa, 0))
 		err(1, "sigaction");
 
+	fix_sa_restorer(sig);
 }
 
 static jmp_buf jmpbuf;

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[PATCH 4.4 00/56] 4.4.69-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 54/56] wlcore: Pass win_size taken from ieee80211_sta to FW Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 34/56] fs/xattr.c: zero out memory copied to userspace in getxattr Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 52/56] mac80211: pass block ack session timeout to to driver Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 42/56] padata: free correct variable Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 56/56] ipmi: Fix kernel panic at ipmi_ssif_thread() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 17/56] usb: hub: Do not attempt to autosuspend disconnected devices Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 24/56] KVM: arm/arm64: fix races in kvm_psci_vcpu_on Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 09/56] staging: vt6656: use off stack for in buffer USB transfers. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 33/56] ext4: evict inline data when writing to memory map Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 51/56] mac80211: pass RX aggregation window size to driver Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 38/56] SMB3: Work around mount failure when using SMB3 dialect to Macs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 55/56] wlcore: Add RX_BA_WIN_SIZE_CHANGE_EVENT event Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 45/56] serial: omap: fix runtime-pm handling on unbind Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 03/56] target/fileio: Fix zero-length READ and WRITE handling Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 50/56] Bluetooth: hci_intel: add missing tty-device sanity check Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 46/56] serial: omap: suspend device on probe errors Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 28/56] vfio/type1: Remove locked page accounting workqueue Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 44/56] serial: samsung: Use right device for DMA-mapping calls Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 36/56] fs/block_dev: always invalidate cleancache in invalidate_bdev() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 08/56] USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 05/56] iscsi-target: Set session_fall_back_to_erl0 when forcing reinstatement Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 12/56] staging: comedi: jr3_pci: fix possible null pointer dereference Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 20/56] selftests/x86/ldt_gdt_32: Work around a glibc sigaction() bug Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 04/56] target: Convert ACL change queue_depth se_session reference usage Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 27/56] dm era: save spacemap metadata root after the pre-commit Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 22/56] um: Fix PTRACE_POKEUSER on x86_64 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 10/56] staging: vt6656: use off stack for out buffer USB transfers. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 18/56] usb: misc: legousbtower: Fix buffers on stack Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 14/56] usb: misc: add missing continue in switch Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 21/56] x86, pmem: Fix cache flushing for iovec write < 8 bytes Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 16/56] usb: hub: Fix error loop seen after hub communication errors Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 15/56] usb: Make sure usb/phy/of gets built-in Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 11/56] staging: gdm724x: gdm_mux: fix use-after-free on module unload Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 29/56] IB/core: Fix sysfs registration error flow Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 19/56] x86/boot: Fix BSS corruption/overwrite bug in early x86 kernel startup Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 25/56] block: fix blk_integrity_register to use templates interval_exp if not 0 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  Re: [PATCH 4.4 00/56] 4.4.69-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-05-18 19:40 +0200
  Re: [PATCH 4.4 00/56] 4.4.69-stable review Guenter Roeck <linux@roeck-us.net> - 2017-05-19 03:20 +0200

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