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    Subject[PATCH 4.4 09/38] ia64: fix user_stack_pointer() for ptrace()
    Date
    From: Sergei Trofimovich <slyfox@gentoo.org>

    commit 7ad1e366167837daeb93d0bacb57dee820b0b898 upstream.

    ia64 has two stacks:

    - memory stack (or stack), pointed at by by r12

    - register backing store (register stack), pointed at by
    ar.bsp/ar.bspstore with complications around dirty
    register frame on CPU.

    In [1] Dmitry noticed that PTRACE_GET_SYSCALL_INFO returns the register
    stack instead memory stack.

    The bug comes from the fact that user_stack_pointer() and
    current_user_stack_pointer() don't return the same register:

    ulong user_stack_pointer(struct pt_regs *regs) { return regs->ar_bspstore; }
    #define current_user_stack_pointer() (current_pt_regs()->r12)

    The change gets both back in sync.

    I think ptrace(PTRACE_GET_SYSCALL_INFO) is the only affected user by
    this bug on ia64.

    The change fixes 'rt_sigreturn.gen.test' strace test where it was
    observed initially.

    Link: https://bugs.gentoo.org/769614 [1]
    Link: https://lkml.kernel.org/r/20210331084447.2561532-1-slyfox@gentoo.org
    Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
    Reported-by: Dmitry V. Levin <ldv@altlinux.org>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/ia64/include/asm/ptrace.h | 8 +-------
    1 file changed, 1 insertion(+), 7 deletions(-)

    --- a/arch/ia64/include/asm/ptrace.h
    +++ b/arch/ia64/include/asm/ptrace.h
    @@ -53,8 +53,7 @@

    static inline unsigned long user_stack_pointer(struct pt_regs *regs)
    {
    - /* FIXME: should this be bspstore + nr_dirty regs? */
    - return regs->ar_bspstore;
    + return regs->r12;
    }

    static inline int is_syscall_success(struct pt_regs *regs)
    @@ -78,11 +77,6 @@ static inline long regs_return_value(str
    unsigned long __ip = instruction_pointer(regs); \
    (__ip & ~3UL) + ((__ip & 3UL) << 2); \
    })
    -/*
    - * Why not default? Because user_stack_pointer() on ia64 gives register
    - * stack backing store instead...
    - */
    -#define current_user_stack_pointer() (current_pt_regs()->r12)

    /* given a pointer to a task_struct, return the user's pt_regs */
    # define task_pt_regs(t) (((struct pt_regs *) ((char *) (t) + IA64_STK_OFFSET)) - 1)

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