lkdtm: Verify that '__ro_after_init' works correctly
The new __ro_after_init section should be writable before init, but not after. Validate that it gets updated at init and can't be written to afterwards. Signed-off-by: Kees Cook <keescook@chromium.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: David Brown <david.brown@linaro.org> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Emese Revfy <re.emese@gmail.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mathias Krause <minipli@googlemail.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: PaX Team <pageexec@freemail.hu> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: kernel-hardening@lists.openwall.com Cc: linux-arch <linux-arch@vger.kernel.org> Link: http://lkml.kernel.org/r/1455748879-21872-6-git-send-email-keescook@chromium.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -103,6 +103,7 @@ enum ctype {
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CT_EXEC_USERSPACE,
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CT_ACCESS_USERSPACE,
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CT_WRITE_RO,
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CT_WRITE_RO_AFTER_INIT,
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CT_WRITE_KERN,
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};
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@ -140,6 +141,7 @@ static char* cp_type[] = {
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"EXEC_USERSPACE",
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"ACCESS_USERSPACE",
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"WRITE_RO",
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"WRITE_RO_AFTER_INIT",
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"WRITE_KERN",
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};
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@ -162,6 +164,7 @@ static DEFINE_SPINLOCK(lock_me_up);
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static u8 data_area[EXEC_SIZE];
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static const unsigned long rodata = 0xAA55AA55;
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static unsigned long ro_after_init __ro_after_init = 0x55AA5500;
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module_param(recur_count, int, 0644);
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MODULE_PARM_DESC(recur_count, " Recursion level for the stack overflow test");
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@ -503,11 +506,28 @@ static void lkdtm_do_action(enum ctype which)
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break;
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}
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case CT_WRITE_RO: {
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unsigned long *ptr;
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/* Explicitly cast away "const" for the test. */
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unsigned long *ptr = (unsigned long *)&rodata;
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ptr = (unsigned long *)&rodata;
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pr_info("attempting bad rodata write at %p\n", ptr);
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*ptr ^= 0xabcd1234;
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pr_info("attempting bad write at %p\n", ptr);
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break;
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}
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case CT_WRITE_RO_AFTER_INIT: {
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unsigned long *ptr = &ro_after_init;
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/*
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* Verify we were written to during init. Since an Oops
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* is considered a "success", a failure is to just skip the
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* real test.
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*/
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if ((*ptr & 0xAA) != 0xAA) {
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pr_info("%p was NOT written during init!?\n", ptr);
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break;
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}
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pr_info("attempting bad ro_after_init write at %p\n", ptr);
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*ptr ^= 0xabcd1234;
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break;
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@ -817,6 +837,9 @@ static int __init lkdtm_module_init(void)
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int n_debugfs_entries = 1; /* Assume only the direct entry */
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int i;
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/* Make sure we can write to __ro_after_init values during __init */
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ro_after_init |= 0xAA;
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/* Register debugfs interface */
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lkdtm_debugfs_root = debugfs_create_dir("provoke-crash", NULL);
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if (!lkdtm_debugfs_root) {
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