x86/ftrace: Set trampoline pages as executable

BugLink: https://bugs.launchpad.net/bugs/1837517
[ 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>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 2ee4b12a70e80ec0fa52d63e24034d069be76d5a..becb075954aa9c7c983c1876219bd277045a64a5 100644 (file)
--- 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);