Revert "x86/fault: BUG() when uaccess helpers fault on kernel addresses"

[linux-2.6-block.git] / arch / x86 / mm / extable.c

diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 6521134057e8f9ef34dbfaf8a0a4e46672a32d3c..856fa409c536408bf6b92039f3c88eeaa8ae53e6 100644 (file)
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -117,67 +117,11 @@ __visible bool ex_handler_fprestore(const struct exception_table_entry *fixup,
 }
 EXPORT_SYMBOL_GPL(ex_handler_fprestore);
 
-/* Helper to check whether a uaccess fault indicates a kernel bug. */
-static bool bogus_uaccess(struct pt_regs *regs, int trapnr,
-                         unsigned long fault_addr)
-{
-       /* This is the normal case: #PF with a fault address in userspace. */
-       if (trapnr == X86_TRAP_PF && fault_addr < TASK_SIZE_MAX)
-               return false;
-
-       /*
-        * This code can be reached for machine checks, but only if the #MC
-        * handler has already decided that it looks like a candidate for fixup.
-        * This e.g. happens when attempting to access userspace memory which
-        * the CPU can't access because of uncorrectable bad memory.
-        */
-       if (trapnr == X86_TRAP_MC)
-               return false;
-
-       /*
-        * There are two remaining exception types we might encounter here:
-        *  - #PF for faulting accesses to kernel addresses
-        *  - #GP for faulting accesses to noncanonical addresses
-        * Complain about anything else.
-        */
-       if (trapnr != X86_TRAP_PF && trapnr != X86_TRAP_GP) {
-               WARN(1, "unexpected trap %d in uaccess\n", trapnr);
-               return false;
-       }
-
-       /*
-        * This is a faulting memory access in kernel space, on a kernel
-        * address, in a usercopy function. This can e.g. be caused by improper
-        * use of helpers like __put_user and by improper attempts to access
-        * userspace addresses in KERNEL_DS regions.
-        * The one (semi-)legitimate exception are probe_kernel_{read,write}(),
-        * which can be invoked from places like kgdb, /dev/mem (for reading)
-        * and privileged BPF code (for reading).
-        * The probe_kernel_*() functions set the kernel_uaccess_faults_ok flag
-        * to tell us that faulting on kernel addresses, and even noncanonical
-        * addresses, in a userspace accessor does not necessarily imply a
-        * kernel bug, root might just be doing weird stuff.
-        */
-       if (current->kernel_uaccess_faults_ok)
-               return false;
-
-       /* This is bad. Refuse the fixup so that we go into die(). */
-       if (trapnr == X86_TRAP_PF) {
-               pr_emerg("BUG: pagefault on kernel address 0x%lx in non-whitelisted uaccess\n",
-                        fault_addr);
-       } else {
-               pr_emerg("BUG: GPF in non-whitelisted uaccess (non-canonical address?)\n");
-       }
-       return true;
-}
-
 __visible bool ex_handler_uaccess(const struct exception_table_entry *fixup,
                                  struct pt_regs *regs, int trapnr,
                                  unsigned long error_code,
                                  unsigned long fault_addr)
 {
-       if (bogus_uaccess(regs, trapnr, fault_addr))
-               return false;
        regs->ip = ex_fixup_addr(fixup);
        return true;
 }
@@ -188,8 +132,6 @@ __visible bool ex_handler_ext(const struct exception_table_entry *fixup,
                              unsigned long error_code,
                              unsigned long fault_addr)
 {
-       if (bogus_uaccess(regs, trapnr, fault_addr))
-               return false;
        /* Special hack for uaccess_err */
        current->thread.uaccess_err = 1;
        regs->ip = ex_fixup_addr(fixup);