From: "Chang S. Bae" <chang.seok.bae@intel.com>
To: Andy Lutomirski <luto@kernel.org>,
"H . Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Markus T Metzger <markus.t.metzger@intel.com>,
"Ravi V . Shankar" <ravi.v.shankar@intel.com>,
"Chang S . Bae" <chang.seok.bae@intel.com>,
linux-kernel@vger.kernel.org
Subject: [PATCH V2 02/15] x86/fsgsbase/64: Make ptrace read FS/GS base accurately
Date: Thu, 31 May 2018 10:58:32 -0700 [thread overview]
Message-ID: <1527789525-8857-3-git-send-email-chang.seok.bae@intel.com> (raw)
In-Reply-To: <1527789525-8857-1-git-send-email-chang.seok.bae@intel.com>
From: Andy Lutomirski <luto@kernel.org>
ptrace can read FS/GS base using the register access API
(PTRACE_PEEKUSER, etc) or PTRACE_ARCH_PRCTL. Make both of these
mechanisms return the actual FS/GS base.
This will improve debuggability by providing the correct information
to ptracer (GDB and etc).
Signed-off-by: Andy Lutomirski <luto@kernel.org>
[chang: Rebase and revise patch description]
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
---
arch/x86/kernel/process_64.c | 59 ++++++++++++++++++++++++++++++++++++--------
1 file changed, 49 insertions(+), 10 deletions(-)
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 5506e1b..e498671 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -279,6 +279,49 @@ static __always_inline void load_seg_legacy(unsigned short prev_index,
}
}
+static unsigned long task_seg_base(struct task_struct *task,
+ unsigned short selector)
+{
+ unsigned short idx = selector >> 3;
+ unsigned long base;
+
+ if (likely((selector & SEGMENT_TI_MASK) == 0)) {
+ if (unlikely(idx >= GDT_ENTRIES))
+ return 0;
+
+ /*
+ * There are no user segments in the GDT with nonzero bases
+ * other than the TLS segments.
+ */
+ if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
+ return 0;
+
+ idx -= GDT_ENTRY_TLS_MIN;
+ base = get_desc_base(&task->thread.tls_array[idx]);
+ } else {
+#ifdef CONFIG_MODIFY_LDT_SYSCALL
+ struct ldt_struct *ldt;
+
+ /*
+ * If performance here mattered, we could protect the LDT
+ * with RCU. This is a slow path, though, so we can just
+ * take the mutex.
+ */
+ mutex_lock(&task->mm->context.lock);
+ ldt = task->mm->context.ldt;
+ if (unlikely(idx >= ldt->nr_entries))
+ base = 0;
+ else
+ base = get_desc_base(ldt->entries + idx);
+ mutex_unlock(&task->mm->context.lock);
+#else
+ base = 0;
+#endif
+ }
+
+ return base;
+}
+
void write_fsbase(unsigned long fsbase)
{
/* set the selector to 0 to not confuse __switch_to */
@@ -299,12 +342,10 @@ unsigned long read_task_fsbase(struct task_struct *task)
if (task == current)
fsbase = read_fsbase();
- else
- /*
- * XXX: This will not behave as expected if called
- * if fsindex != 0
- */
+ else if (task->thread.fsindex == 0)
fsbase = task->thread.fsbase;
+ else
+ fsbase = task_seg_base(task, task->thread.fsindex);
return fsbase;
}
@@ -315,12 +356,10 @@ unsigned long read_task_gsbase(struct task_struct *task)
if (task == current)
gsbase = read_inactive_gsbase();
- else
- /*
- * XXX: This will not behave as expected if called
- * if gsindex != 0
- */
+ else if (task->thread.gsindex == 0)
gsbase = task->thread.gsbase;
+ else
+ gsbase = task_seg_base(task, task->thread.gsindex);
return gsbase;
}
--
2.7.4
next prev parent reply other threads:[~2018-05-31 17:59 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-31 17:58 [PATCH V2 00/15] x86: Enable FSGSBASE instructions Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 01/15] x86/fsgsbase/64: Introduce FS/GS base helper functions Chang S. Bae
2018-05-31 20:14 ` Andy Lutomirski
2018-05-31 21:03 ` Bae, Chang Seok
2018-05-31 17:58 ` Chang S. Bae [this message]
2018-05-31 20:14 ` [PATCH V2 02/15] x86/fsgsbase/64: Make ptrace read FS/GS base accurately Andy Lutomirski
2018-05-31 20:31 ` hpa
2018-05-31 20:38 ` Andy Lutomirski
2018-05-31 17:58 ` [PATCH V2 03/15] x86/fsgsbase/64: Use FS/GS base helpers in core dump Chang S. Bae
2018-05-31 20:15 ` Andy Lutomirski
2018-05-31 21:03 ` Bae, Chang Seok
2018-05-31 17:58 ` [PATCH V2 04/15] x86/fsgsbase/64: Factor out load FS/GS segments from __switch_to Chang S. Bae
2018-05-31 20:16 ` Andy Lutomirski
2018-05-31 17:58 ` [PATCH V2 05/15] x86/vdso: Move out the CPU number store Chang S. Bae
2018-05-31 20:25 ` Andy Lutomirski
2018-05-31 21:06 ` Bae, Chang Seok
2018-06-05 7:02 ` [lkp-robot] [x86/vdso] f52001961d: BUG:kernel_hang_in_early-boot_stage,last_printk:Probing_EDD(edd=off_to_disable)...ok kernel test robot
2018-05-31 17:58 ` [PATCH V2 06/15] taint: Add taint for insecure Chang S. Bae
2018-05-31 20:25 ` Andy Lutomirski
2018-05-31 20:50 ` hpa
2018-05-31 17:58 ` [PATCH V2 07/15] x86/fsgsbase/64: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 08/15] x86/fsgsbase/64: Add intrinsics/macros for FSGSBASE instructions Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 09/15] x86/fsgsbase/64: Enable FSGSBASE instructions in helper functions Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 10/15] x86/fsgsbase/64: Preserve FS/GS state in __switch_to if FSGSBASE is on Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 11/15] x86/fsgsbase/64: When copying a thread, use FSGSBASE if enabled Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 12/15] x86/fsgsbase/64: Use per-CPU base as GS base on paranoid_entry Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 13/15] x86/fsgsbase/64: Enable FSGSBASE by default and add a chicken bit Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 14/15] x86/elf: Enumerate kernel FSGSBASE capability in AT_HWCAP2 Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 15/15] x86/fsgsbase/64: Add documentation for FSGSBASE Chang S. Bae
2018-05-31 20:37 ` [PATCH V2 00/15] x86: Enable FSGSBASE instructions Andy Lutomirski
2018-05-31 21:11 ` Bae, Chang Seok
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