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    Subject[PATCH 5.15 097/106] cfi: Fix __cfi_slowpath_diag RCU usage with cpuidle
    Date
    From: Sami Tolvanen <samitolvanen@google.com>

    commit 57cd6d157eb479f0a8e820fd36b7240845c8a937 upstream.

    RCU_NONIDLE usage during __cfi_slowpath_diag can result in an invalid
    RCU state in the cpuidle code path:

    WARNING: CPU: 1 PID: 0 at kernel/rcu/tree.c:613 rcu_eqs_enter+0xe4/0x138
    ...
    Call trace:
    rcu_eqs_enter+0xe4/0x138
    rcu_idle_enter+0xa8/0x100
    cpuidle_enter_state+0x154/0x3a8
    cpuidle_enter+0x3c/0x58
    do_idle.llvm.6590768638138871020+0x1f4/0x2ec
    cpu_startup_entry+0x28/0x2c
    secondary_start_kernel+0x1b8/0x220
    __secondary_switched+0x94/0x98

    Instead, call rcu_irq_enter/exit to wake up RCU only when needed and
    disable interrupts for the entire CFI shadow/module check when we do.

    Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
    Link: https://lore.kernel.org/r/20220531175910.890307-1-samitolvanen@google.com
    Fixes: cf68fffb66d6 ("add support for Clang CFI")
    Cc: stable@vger.kernel.org
    Signed-off-by: Kees Cook <keescook@chromium.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    kernel/cfi.c | 22 ++++++++++++++++------
    1 file changed, 16 insertions(+), 6 deletions(-)

    --- a/kernel/cfi.c
    +++ b/kernel/cfi.c
    @@ -281,6 +281,8 @@ static inline cfi_check_fn find_module_c
    static inline cfi_check_fn find_check_fn(unsigned long ptr)
    {
    cfi_check_fn fn = NULL;
    + unsigned long flags;
    + bool rcu_idle;

    if (is_kernel_text(ptr))
    return __cfi_check;
    @@ -290,13 +292,21 @@ static inline cfi_check_fn find_check_fn
    * the shadow and __module_address use RCU, so we need to wake it
    * up if necessary.
    */
    - RCU_NONIDLE({
    - if (IS_ENABLED(CONFIG_CFI_CLANG_SHADOW))
    - fn = find_shadow_check_fn(ptr);
    + rcu_idle = !rcu_is_watching();
    + if (rcu_idle) {
    + local_irq_save(flags);
    + rcu_irq_enter();
    + }

    - if (!fn)
    - fn = find_module_check_fn(ptr);
    - });
    + if (IS_ENABLED(CONFIG_CFI_CLANG_SHADOW))
    + fn = find_shadow_check_fn(ptr);
    + if (!fn)
    + fn = find_module_check_fn(ptr);
    +
    + if (rcu_idle) {
    + rcu_irq_exit();
    + local_irq_restore(flags);
    + }

    return fn;
    }

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