• Yonghong Song's avatar
    x86/idt: Remove X86_TRAP_BP initialization in idt_setup_traps() · d0cd64b0
    Yonghong Song authored
    Commit b70543a0("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: b70543a0
    
    ("x86/idt: Move regular trap init to tables")
    Reported-and-tested-by: default avatarYonghong Song <yhs@fb.com>
    Signed-off-by: default avatarYonghong Song <yhs@fb.com>
    Signed-off-by: default avatarThomas 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
    d0cd64b0
idt.c 9.47 KB