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    Subject[PATCH 5.4 78/90] x86/unwind/orc: Fix premature unwind stoppage due to IRET frames
    Date
    From: Josh Poimboeuf <jpoimboe@redhat.com>

    commit 81b67439d147677d844d492fcbd03712ea438f42 upstream.

    The following execution path is possible:

    fsnotify()
    [ realign the stack and store previous SP in R10 ]
    <IRQ>
    [ only IRET regs saved ]
    common_interrupt()
    interrupt_entry()
    <NMI>
    [ full pt_regs saved ]
    ...
    [ unwind stack ]

    When the unwinder goes through the NMI and the IRQ on the stack, and
    then sees fsnotify(), it doesn't have access to the value of R10,
    because it only has the five IRET registers. So the unwind stops
    prematurely.

    However, because the interrupt_entry() code is careful not to clobber
    R10 before saving the full regs, the unwinder should be able to read R10
    from the previously saved full pt_regs associated with the NMI.

    Handle this case properly. When encountering an IRET regs frame
    immediately after a full pt_regs frame, use the pt_regs as a backup
    which can be used to get the C register values.

    Also, note that a call frame resets the 'prev_regs' value, because a
    function is free to clobber the registers. For this fix to work, the
    IRET and full regs frames must be adjacent, with no FUNC frames in
    between. So replace the FUNC hint in interrupt_entry() with an
    IRET_REGS hint.

    Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder")
    Reviewed-by: Miroslav Benes <mbenes@suse.cz>
    Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Dave Jones <dsj@fb.com>
    Cc: Jann Horn <jannh@google.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Vince Weaver <vincent.weaver@maine.edu>
    Link: https://lore.kernel.org/r/97a408167cc09f1cfa0de31a7b70dd88868d743f.1587808742.git.jpoimboe@redhat.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/entry/entry_64.S | 4 +--
    arch/x86/include/asm/unwind.h | 2 -
    arch/x86/kernel/unwind_orc.c | 51 ++++++++++++++++++++++++++++++++----------
    3 files changed, 43 insertions(+), 14 deletions(-)

    --- a/arch/x86/entry/entry_64.S
    +++ b/arch/x86/entry/entry_64.S
    @@ -512,7 +512,7 @@ END(spurious_entries_start)
    * +----------------------------------------------------+
    */
    ENTRY(interrupt_entry)
    - UNWIND_HINT_FUNC
    + UNWIND_HINT_IRET_REGS offset=16
    ASM_CLAC
    cld

    @@ -544,9 +544,9 @@ ENTRY(interrupt_entry)
    pushq 5*8(%rdi) /* regs->eflags */
    pushq 4*8(%rdi) /* regs->cs */
    pushq 3*8(%rdi) /* regs->ip */
    + UNWIND_HINT_IRET_REGS
    pushq 2*8(%rdi) /* regs->orig_ax */
    pushq 8(%rdi) /* return address */
    - UNWIND_HINT_FUNC

    movq (%rdi), %rdi
    jmp 2f
    --- a/arch/x86/include/asm/unwind.h
    +++ b/arch/x86/include/asm/unwind.h
    @@ -19,7 +19,7 @@ struct unwind_state {
    #if defined(CONFIG_UNWINDER_ORC)
    bool signal, full_regs;
    unsigned long sp, bp, ip;
    - struct pt_regs *regs;
    + struct pt_regs *regs, *prev_regs;
    #elif defined(CONFIG_UNWINDER_FRAME_POINTER)
    bool got_irq;
    unsigned long *bp, *orig_sp, ip;
    --- a/arch/x86/kernel/unwind_orc.c
    +++ b/arch/x86/kernel/unwind_orc.c
    @@ -375,9 +375,38 @@ static bool deref_stack_iret_regs(struct
    return true;
    }

    +/*
    + * If state->regs is non-NULL, and points to a full pt_regs, just get the reg
    + * value from state->regs.
    + *
    + * Otherwise, if state->regs just points to IRET regs, and the previous frame
    + * had full regs, it's safe to get the value from the previous regs. This can
    + * happen when early/late IRQ entry code gets interrupted by an NMI.
    + */
    +static bool get_reg(struct unwind_state *state, unsigned int reg_off,
    + unsigned long *val)
    +{
    + unsigned int reg = reg_off/8;
    +
    + if (!state->regs)
    + return false;
    +
    + if (state->full_regs) {
    + *val = ((unsigned long *)state->regs)[reg];
    + return true;
    + }
    +
    + if (state->prev_regs) {
    + *val = ((unsigned long *)state->prev_regs)[reg];
    + return true;
    + }
    +
    + return false;
    +}
    +
    bool unwind_next_frame(struct unwind_state *state)
    {
    - unsigned long ip_p, sp, orig_ip = state->ip, prev_sp = state->sp;
    + unsigned long ip_p, sp, tmp, orig_ip = state->ip, prev_sp = state->sp;
    enum stack_type prev_type = state->stack_info.type;
    struct orc_entry *orc;
    bool indirect = false;
    @@ -439,39 +468,35 @@ bool unwind_next_frame(struct unwind_sta
    break;

    case ORC_REG_R10:
    - if (!state->regs || !state->full_regs) {
    + if (!get_reg(state, offsetof(struct pt_regs, r10), &sp)) {
    orc_warn("missing regs for base reg R10 at ip %pB\n",
    (void *)state->ip);
    goto err;
    }
    - sp = state->regs->r10;
    break;

    case ORC_REG_R13:
    - if (!state->regs || !state->full_regs) {
    + if (!get_reg(state, offsetof(struct pt_regs, r13), &sp)) {
    orc_warn("missing regs for base reg R13 at ip %pB\n",
    (void *)state->ip);
    goto err;
    }
    - sp = state->regs->r13;
    break;

    case ORC_REG_DI:
    - if (!state->regs || !state->full_regs) {
    + if (!get_reg(state, offsetof(struct pt_regs, di), &sp)) {
    orc_warn("missing regs for base reg DI at ip %pB\n",
    (void *)state->ip);
    goto err;
    }
    - sp = state->regs->di;
    break;

    case ORC_REG_DX:
    - if (!state->regs || !state->full_regs) {
    + if (!get_reg(state, offsetof(struct pt_regs, dx), &sp)) {
    orc_warn("missing regs for base reg DX at ip %pB\n",
    (void *)state->ip);
    goto err;
    }
    - sp = state->regs->dx;
    break;

    default:
    @@ -498,6 +523,7 @@ bool unwind_next_frame(struct unwind_sta

    state->sp = sp;
    state->regs = NULL;
    + state->prev_regs = NULL;
    state->signal = false;
    break;

    @@ -509,6 +535,7 @@ bool unwind_next_frame(struct unwind_sta
    }

    state->regs = (struct pt_regs *)sp;
    + state->prev_regs = NULL;
    state->full_regs = true;
    state->signal = true;
    break;
    @@ -520,6 +547,8 @@ bool unwind_next_frame(struct unwind_sta
    goto err;
    }

    + if (state->full_regs)
    + state->prev_regs = state->regs;
    state->regs = (void *)sp - IRET_FRAME_OFFSET;
    state->full_regs = false;
    state->signal = true;
    @@ -534,8 +563,8 @@ bool unwind_next_frame(struct unwind_sta
    /* Find BP: */
    switch (orc->bp_reg) {
    case ORC_REG_UNDEFINED:
    - if (state->regs && state->full_regs)
    - state->bp = state->regs->bp;
    + if (get_reg(state, offsetof(struct pt_regs, bp), &tmp))
    + state->bp = tmp;
    break;

    case ORC_REG_PREV_SP:

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