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From: tip-bot for Andy Lutomirski <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: mingo@kernel.org, riel@surriel.com, brgerst@gmail.com,
	dave.hansen@linux.intel.com, bp@alien8.de, tglx@linutronix.de,
	hpa@zytor.com, linux-kernel@vger.kernel.org,
	chang.seok.bae@intel.com, luto@kernel.org,
	torvalds@linux-foundation.org, dvlasenk@redhat.com,
	ravi.v.shankar@intel.com, peterz@infradead.org,
	markus.t.metzger@intel.com, luto@amacapital.net
Subject: [tip:x86/asm] x86/fsgsbase/64: Fix ptrace() to read the FS/GS base accurately
Date: Mon, 8 Oct 2018 02:54:51 -0700	[thread overview]
Message-ID: <tip-07e1d88adaaeab247b300926f78cc3f950dbeda3@git.kernel.org> (raw)
In-Reply-To: <1537312139-5580-2-git-send-email-chang.seok.bae@intel.com>

Commit-ID:  07e1d88adaaeab247b300926f78cc3f950dbeda3
Gitweb:     https://git.kernel.org/tip/07e1d88adaaeab247b300926f78cc3f950dbeda3
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Tue, 18 Sep 2018 16:08:52 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 8 Oct 2018 10:41:08 +0200

x86/fsgsbase/64: Fix ptrace() to read the FS/GS base accurately

On 64-bit kernels ptrace can read the FS/GS base using the register access
APIs (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 such as GDB.

[ chang: Rebased and revised patch description. ]
[ mingo: Revised the changelog some more. ]

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Markus T Metzger <markus.t.metzger@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Shankar <ravi.v.shankar@intel.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1537312139-5580-2-git-send-email-chang.seok.bae@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/ptrace.c | 62 ++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 52 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index e2ee403865eb..3acbf45cb7fb 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -39,6 +39,7 @@
 #include <asm/hw_breakpoint.h>
 #include <asm/traps.h>
 #include <asm/syscall.h>
+#include <asm/mmu_context.h>
 
 #include "tls.h"
 
@@ -342,6 +343,49 @@ static int set_segment_reg(struct task_struct *task,
 	return 0;
 }
 
+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;
+}
+
 #endif	/* CONFIG_X86_32 */
 
 static unsigned long get_flags(struct task_struct *task)
@@ -435,18 +479,16 @@ static unsigned long getreg(struct task_struct *task, unsigned long offset)
 
 #ifdef CONFIG_X86_64
 	case offsetof(struct user_regs_struct, fs_base): {
-		/*
-		 * XXX: This will not behave as expected if called on
-		 * current or if fsindex != 0.
-		 */
-		return task->thread.fsbase;
+		if (task->thread.fsindex == 0)
+			return task->thread.fsbase;
+		else
+			return task_seg_base(task, task->thread.fsindex);
 	}
 	case offsetof(struct user_regs_struct, gs_base): {
-		/*
-		 * XXX: This will not behave as expected if called on
-		 * current or if fsindex != 0.
-		 */
-		return task->thread.gsbase;
+		if (task->thread.gsindex == 0)
+			return task->thread.gsbase;
+		else
+			return task_seg_base(task, task->thread.gsindex);
 	}
 #endif
 	}

  reply	other threads:[~2018-10-08  9:56 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-18 23:08 [PATCH v6 0/8] x86: infrastructure to enable FSGSBASE Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 1/8] x86/arch_prctl/64: Make ptrace read FS/GS base accurately Chang S. Bae
2018-10-08  9:54   ` tip-bot for Andy Lutomirski [this message]
2018-10-08  9:59   ` [tip:x86/asm] x86/segments: Introduce the 'CPUNODE' naming to better document the segment limit CPU/node NR trick tip-bot for Ingo Molnar
2018-10-08  9:59   ` [tip:x86/asm] x86/fsgsbase/64: Clean up various details tip-bot for Ingo Molnar
2018-09-18 23:08 ` [PATCH v6 2/8] x86/fsgsbase/64: Introduce FS/GS base helper functions Chang S. Bae
2018-10-08  9:55   ` [tip:x86/asm] " tip-bot for Chang S. Bae
2018-10-24 19:01   ` [regression in -rc1] Re: [PATCH v6 2/8] " Andy Lutomirski
2018-10-24 19:13     ` Bae, Chang Seok
2018-10-24 19:22       ` Andy Lutomirski
2018-10-24 19:29         ` Bae, Chang Seok
2018-10-24 19:43           ` Andy Lutomirski
2018-10-24 22:50             ` Bae, Chang Seok
2018-10-25 22:37     ` Andy Lutomirski
2018-09-18 23:08 ` [PATCH v6 3/8] x86/fsgsbase/64: Make ptrace use correct FS/GS base helpers Chang S. Bae
2018-10-08  9:56   ` [tip:x86/asm] x86/fsgsbase/64: Make ptrace use the new " tip-bot for Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 4/8] x86/fsgsbase/64: Use FS/GS base helpers in core dump Chang S. Bae
2018-10-08  9:56   ` [tip:x86/asm] x86/fsgsbase/64: Convert the ELF core dump code to the new FSGSBASE helpers tip-bot for Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 5/8] x86/fsgsbase/64: Factor out load FS/GS segments from __switch_to() Chang S. Bae
2018-10-08  9:57   ` [tip:x86/asm] x86/fsgsbase/64: Factor out FS/GS segment loading " tip-bot for Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 6/8] x86/segments/64: Rename PER_CPU segment to CPU_NUMBER Chang S. Bae
2018-10-08  9:57   ` [tip:x86/asm] x86/segments/64: Rename the GDT PER_CPU entry " tip-bot for Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 7/8] x86/vdso: Introduce helper functions for CPU and node number Chang S. Bae
2018-10-08  9:58   ` [tip:x86/asm] " tip-bot for Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 8/8] x86/vdso: Move out the CPU initialization Chang S. Bae
2018-10-08  8:36   ` Ingo Molnar
2018-10-08  9:58   ` [tip:x86/asm] x86/vdso: Initialize the CPU/node NR segment descriptor earlier tip-bot for Chang S. Bae

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