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    Subject[PATCH] x86/unwind/orc: Handle kretprobes_trampoline
    Date
    From: Marios Pomonis <pomonis@google.com>

    Fix a bug in the ORC unwinder when kretprobes has replaced a return
    address with the address of `kretprobes_trampoline'. ORC mistakenly
    assumes that the address in the stack is a return address and decrements
    it by 1 in order to find the proper depth of the next frame.

    This issue was discovered while testing the FG-KASLR series[0][1] and
    running the live patching test[2] that was originally failing[3].

    [0] https://lore.kernel.org/kernel-hardening/20200923173905.11219-1-kristen@linux.intel.com/
    [1] https://github.com/KSPP/linux/issues/132
    [2] https://github.com/lpechacek/qa_test_klp
    [3] https://lore.kernel.org/lkml/alpine.LSU.2.21.2009251450260.13615@pobox.suse.cz/

    Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder")
    Signed-off-by: Marios Pomonis <pomonis@google.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Alexander Lobakin <alexandr.lobakin@intel.com>
    Cc: Kristen C Accardi <kristen.c.accardi@intel.com>
    Cc: Sami Tolvanen <samitolvanen@google.com>
    Signed-off-by: Kees Cook <keescook@chromium.org>
    ---
    arch/x86/kernel/unwind_orc.c | 12 +++++++++++-
    1 file changed, 11 insertions(+), 1 deletion(-)

    diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
    index a1202536fc57..8c5038b3b707 100644
    --- a/arch/x86/kernel/unwind_orc.c
    +++ b/arch/x86/kernel/unwind_orc.c
    @@ -7,6 +7,7 @@
    #include <asm/unwind.h>
    #include <asm/orc_types.h>
    #include <asm/orc_lookup.h>
    +#include <asm/kprobes.h>

    #define orc_warn(fmt, ...) \
    printk_deferred_once(KERN_WARNING "WARNING: " fmt, ##__VA_ARGS__)
    @@ -414,6 +415,15 @@ static bool get_reg(struct unwind_state *state, unsigned int reg_off,
    return false;
    }

    +static bool is_kretprobe_trampoline(unsigned long ip)
    +{
    +#ifdef CONFIG_KRETPROBES
    + if (ip == (unsigned long)&kretprobe_trampoline)
    + return true;
    +#endif
    + return false;
    +}
    +
    bool unwind_next_frame(struct unwind_state *state)
    {
    unsigned long ip_p, sp, tmp, orig_ip = state->ip, prev_sp = state->sp;
    @@ -540,7 +550,7 @@ bool unwind_next_frame(struct unwind_state *state)
    state->sp = sp;
    state->regs = NULL;
    state->prev_regs = NULL;
    - state->signal = false;
    + state->signal = is_kretprobe_trampoline(state->ip);
    break;

    case UNWIND_HINT_TYPE_REGS:
    --
    2.30.2
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