[RESEND PATCH tip] x86/idt: Remove X86_TRAP_BP initialization in idt_setup_traps()

[RESEND PATCH tip] x86/idt: Remove X86_TRAP_BP initialization in idt_setup_traps()

[Yonghong Song]

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 original change and it breaks
uprobe functionality for x86_32. A program with uprobe
instrumented can have segfault on x86_32 instead of normal finish.
Uprobe still works on x86_64 even with this commit.

This patch removes X86_TRAP_BP from the structure def_idts
which is used in idt_setup_traps(). It also removes a redundant
entry for X86_TRAP_NMI in def_idts. Tested on both x86_64 and x86_32,
uprobe works fine.

Fixes: b70543a0b2b6("x86/idt: Move regular trap init to tables")
Reported-and-tested-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 arch/x86/kernel/idt.c | 2 --
 1 file changed, 2 deletions(-)

[RESEND with adding linux-kernel@vger.kernel.org as the recipient.]

diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
index 723fa97..d985cef 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),
-- 
2.9.5

[tip:x86/urgent] x86/idt: Remove X86_TRAP_BP initialization in idt_setup_traps()

[tip-bot for Yonghong Song]

Commit-ID:  d0cd64b02aa854d68ce517cb7da1fe4e4fff2653
Gitweb:     https://git.kernel.org/tip/d0cd64b02aa854d68ce517cb7da1fe4e4fff2653
Author:     Yonghong Song <yhs@fb.com>
AuthorDate: Wed, 8 Nov 2017 11:28:45 -0800
Committer:  Thomas Gleixner <tglx@linutronix.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@fb.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: a.p.zijlstra@chello.nl
Cc: ast@fb.com
Cc: oleg@redhat.com
Cc: luto@kernel.org
Cc: kernel-team@fb.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),