linux-kernel - [tip:x86/urgent] x86/idt: Remove X86_TRAP_BP initialization in idt_setup

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Date:   Wed, 8 Nov 2017 12:10:03 -0800
From:   tip-bot for Yonghong Song <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, linux-kernel@...r.kernel.org, yhs@...com,
        mingo@...nel.org, tglx@...utronix.de
Subject: [tip:x86/urgent] x86/idt: Remove X86_TRAP_BP initialization in
 idt_setup_traps()

Commit-ID:  d0cd64b02aa854d68ce517cb7da1fe4e4fff2653
Gitweb:     https://git.kernel.org/tip/d0cd64b02aa854d68ce517cb7da1fe4e4fff2653
Author:     Yonghong Song <yhs@...com>
AuthorDate: Wed, 8 Nov 2017 11:28:45 -0800
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Wed, 8 Nov 2017 21:05:23 +0100

x86/idt: Remove X86_TRAP_BP initialization in idt_setup_traps()

Commit b70543a0b2b6("x86/idt: Move regular trap init to tables") moves
regular trap init for each trap vector into a table based
initialization. It introduced the initialization for vector X86_TRAP_BP
which was not in the code which it replaced. This breaks uprobe
functionality for x86_32; the probed program segfaults instead of handling
the probe proper.

The reason for this is that TRAP_BP is set up as system interrupt gate
(DPL3) in the early IDT and then replaced by a regular interrupt gate
(DPL0) in idt_setup_traps(). The DPL0 restriction causes the int3 trap
to fail with a #GP resulting in a SIGSEGV of the probed program.

On 64bit this does not cause a problem because the IDT entry is replaced
with a system interrupt gate (DPL3) with interrupt stack afterwards.

Remove X86_TRAP_BP from the def_idts table which is used in
idt_setup_traps(). Remove a redundant entry for X86_TRAP_NMI in def_idts
while at it. Tested on both x86_64 and x86_32.

[ tglx: Amended changelog with a description of the root cause ]

Fixes: b70543a0b2b6("x86/idt: Move regular trap init to tables")
Reported-and-tested-by: Yonghong Song <yhs@...com>
Signed-off-by: Yonghong Song <yhs@...com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: a.p.zijlstra@...llo.nl
Cc: ast@...com
Cc: oleg@...hat.com
Cc: luto@...nel.org
Cc: kernel-team@...com
Link: https://lkml.kernel.org/r/20171108192845.552709-1-yhs@fb.com

---
 arch/x86/kernel/idt.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
index 6107ee1..014cb2f 100644
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -92,8 +92,6 @@ static const __initdata struct idt_data def_idts[] = {
 	INTG(X86_TRAP_DF,		double_fault),
 #endif
 	INTG(X86_TRAP_DB,		debug),
-	INTG(X86_TRAP_NMI,		nmi),
-	INTG(X86_TRAP_BP,		int3),

 #ifdef CONFIG_X86_MCE
 	INTG(X86_TRAP_MC,		&machine_check),