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| author | Andy Lutomirski <luto@kernel.org> | 2019-06-26 21:45:05 -0700 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2019-06-28 00:04:39 +0200 |
| commit | e0a446ce394a7915f2ffc03f9bb610c5ac4dbbf1 (patch) | |
| tree | a2458144d3b24a798ebe5632e8efdb9002df5154 /arch | |
| parent | 918ce325098a4eef99daad7b6796da33cebaf03a (diff) | |
| download | linux-e0a446ce394a7915f2ffc03f9bb610c5ac4dbbf1.tar.bz2 | |
x86/vsyscall: Document odd SIGSEGV error code for vsyscalls
Even if vsyscall=none, user page faults on the vsyscall page are reported
as though the PROT bit in the error code was set. Add a comment explaining
why this is probably okay and display the value in the test case.
While at it, explain why the behavior is correct with respect to PKRU.
Modify also the selftest to print the odd error code so that there is a
way to demonstrate the odd behaviour.
If anyone really cares about more accurate emulation, the behaviour could
be changed. But that needs a real good justification.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/75c91855fd850649ace162eec5495a1354221aaa.1561610354.git.luto@kernel.org
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/mm/fault.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 288a5462076f..58e4f1f00bbc 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -710,6 +710,10 @@ static void set_signal_archinfo(unsigned long address, * To avoid leaking information about the kernel page * table layout, pretend that user-mode accesses to * kernel addresses are always protection faults. + * + * NB: This means that failed vsyscalls with vsyscall=none + * will have the PROT bit. This doesn't leak any + * information and does not appear to cause any problems. */ if (address >= TASK_SIZE_MAX) error_code |= X86_PF_PROT; @@ -1375,6 +1379,9 @@ void do_user_addr_fault(struct pt_regs *regs, * * The vsyscall page does not have a "real" VMA, so do this * emulation before we go searching for VMAs. + * + * PKRU never rejects instruction fetches, so we don't need + * to consider the PF_PK bit. */ if (is_vsyscall_vaddr(address)) { if (emulate_vsyscall(hw_error_code, regs, address)) |