Merge branch 'x86-uaccess-cleanup': x86 uaccess header cleanups

Merge my x86 uaccess updates branch.

The LAM ("Linear Address Masking") updates in this release made me
unhappy about how "access_ok()" was done, and it actually turned out to
have a couple of small bugs in it too.  This is my cleanup of the code:

 - use the sign bit of the __user pointer rather than masking the
   address and checking it against the TASK_SIZE range.

   We already did this part for the get/put_user() side, but
   'access_ok()' did the naïve "mask and range check" thing, which not
   only generates nasty code, but also ended up meaning that __access_ok
   itself didn't do a good job, and so copy_from_user_nmi() didn't get
   the check right.

 - move all the code that is 64-bit only into the 64-bit version of the
   header file, so that we don't unnecessarily pollute the shared x86
   code and make it look like LAM might work in 32-bit too.

 - fix a bug in the address masking (that doesn't end up mattering: in
   this case the fix was to just remove the buggy code entirely).

 - a couple of trivial cleanups and added commentary about the
   access_ok() rules.

* x86-uaccess-cleanup:
  x86-64: mm: clarify the 'positive addresses' user address rules
  x86: mm: remove 'sign' games from LAM untagged_addr*() macros
  x86: uaccess: move 32-bit and 64-bit parts into proper <asm/uaccess_N.h> header
  x86: mm: remove architecture-specific 'access_ok()' define
  x86-64: make access_ok() independent of LAM

1 files changed, 34 insertions, 6 deletions

diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 60814e110a54..271dcb2deabc 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -130,10 +130,36 @@ static bool ex_handler_fprestore(const struct exception_table_entry *fixup,
 	return true;
 }
 
+/*
+ * On x86-64, we end up being imprecise with 'access_ok()', and allow
+ * non-canonical user addresses to make the range comparisons simpler,
+ * and to not have to worry about LAM being enabled.
+ *
+ * In fact, we allow up to one page of "slop" at the sign boundary,
+ * which means that we can do access_ok() by just checking the sign
+ * of the pointer for the common case of having a small access size.
+ */
+static bool gp_fault_address_ok(unsigned long fault_address)
+{
+#ifdef CONFIG_X86_64
+	/* Is it in the "user space" part of the non-canonical space? */
+	if (valid_user_address(fault_address))
+		return true;
+
+	/* .. or just above it? */
+	fault_address -= PAGE_SIZE;
+	if (valid_user_address(fault_address))
+		return true;
+#endif
+	return false;
+}
+
 static bool ex_handler_uaccess(const struct exception_table_entry *fixup,
-			       struct pt_regs *regs, int trapnr)
+			       struct pt_regs *regs, int trapnr,
+			       unsigned long fault_address)
 {
-	WARN_ONCE(trapnr == X86_TRAP_GP, "General protection fault in user access. Non-canonical address?");
+	WARN_ONCE(trapnr == X86_TRAP_GP && !gp_fault_address_ok(fault_address),
+		"General protection fault in user access. Non-canonical address?");
 	return ex_handler_default(fixup, regs);
 }
 
@@ -189,10 +215,12 @@ static bool ex_handler_imm_reg(const struct exception_table_entry *fixup,
 }
 
 static bool ex_handler_ucopy_len(const struct exception_table_entry *fixup,
-				  struct pt_regs *regs, int trapnr, int reg, int imm)
+				  struct pt_regs *regs, int trapnr,
+				  unsigned long fault_address,
+				  int reg, int imm)
 {
 	regs->cx = imm * regs->cx + *pt_regs_nr(regs, reg);
-	return ex_handler_uaccess(fixup, regs, trapnr);
+	return ex_handler_uaccess(fixup, regs, trapnr, fault_address);
 }
 
 int ex_get_fixup_type(unsigned long ip)
@@ -238,7 +266,7 @@ int fixup_exception(struct pt_regs *regs, int trapnr, unsigned long error_code,
 	case EX_TYPE_FAULT_MCE_SAFE:
 		return ex_handler_fault(e, regs, trapnr);
 	case EX_TYPE_UACCESS:
-		return ex_handler_uaccess(e, regs, trapnr);
+		return ex_handler_uaccess(e, regs, trapnr, fault_addr);
 	case EX_TYPE_COPY:
 		return ex_handler_copy(e, regs, trapnr);
 	case EX_TYPE_CLEAR_FS:
@@ -269,7 +297,7 @@ int fixup_exception(struct pt_regs *regs, int trapnr, unsigned long error_code,
 	case EX_TYPE_FAULT_SGX:
 		return ex_handler_sgx(e, regs, trapnr);
 	case EX_TYPE_UCOPY_LEN:
-		return ex_handler_ucopy_len(e, regs, trapnr, reg, imm);
+		return ex_handler_ucopy_len(e, regs, trapnr, fault_addr, reg, imm);
 	case EX_TYPE_ZEROPAD:
 		return ex_handler_zeropad(e, regs, fault_addr);
 	}