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    Subject[PATCH 5.0 079/346] x86/ftrace: Set trampoline pages as executable
    Date
    [ Upstream commit 3c0dab44e22782359a0a706cbce72de99a22aa75 ]

    Since alloc_module() will not set the pages as executable soon, set
    ftrace trampoline pages as executable after they are allocated.

    For the time being, do not change ftrace to use the text_poke()
    interface. As a result, ftrace still breaks W^X.

    Signed-off-by: Nadav Amit <namit@vmware.com>
    Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
    Cc: <akpm@linux-foundation.org>
    Cc: <ard.biesheuvel@linaro.org>
    Cc: <deneen.t.dock@intel.com>
    Cc: <kernel-hardening@lists.openwall.com>
    Cc: <kristen@linux.intel.com>
    Cc: <linux_dti@icloud.com>
    Cc: <will.deacon@arm.com>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Rik van Riel <riel@surriel.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: https://lkml.kernel.org/r/20190426001143.4983-10-namit@vmware.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/kernel/ftrace.c | 8 ++++++++
    1 file changed, 8 insertions(+)

    diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
    index 2ee4b12a70e80..becb075954aa9 100644
    --- a/arch/x86/kernel/ftrace.c
    +++ b/arch/x86/kernel/ftrace.c
    @@ -748,6 +748,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
    unsigned long end_offset;
    unsigned long op_offset;
    unsigned long offset;
    + unsigned long npages;
    unsigned long size;
    unsigned long retq;
    unsigned long *ptr;
    @@ -780,6 +781,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
    return 0;

    *tramp_size = size + RET_SIZE + sizeof(void *);
    + npages = DIV_ROUND_UP(*tramp_size, PAGE_SIZE);

    /* Copy ftrace_caller onto the trampoline memory */
    ret = probe_kernel_read(trampoline, (void *)start_offset, size);
    @@ -824,6 +826,12 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
    /* ALLOC_TRAMP flags lets us know we created it */
    ops->flags |= FTRACE_OPS_FL_ALLOC_TRAMP;

    + /*
    + * Module allocation needs to be completed by making the page
    + * executable. The page is still writable, which is a security hazard,
    + * but anyhow ftrace breaks W^X completely.
    + */
    + set_memory_x((unsigned long)trampoline, npages);
    return (unsigned long)trampoline;
    fail:
    tramp_free(trampoline, *tramp_size);
    --
    2.20.1


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