[PATCH] x86/extable: ensure entries are swapped completely when sorting

[Mathias Krause]

The x86 exception table sorting was changed in commit 29934b0fb8ff
("x86/extable: use generic search and sort routines") to use the arch
independent code in lib/extable.c. However, the patch was mangled
somehow on its way into the kernel from the last version posted at [1].
The committed version kind of attempted to incorporate the changes of
commit 548acf19234d ("x86/mm: Expand the exception table logic to allow
new handling options") as in _completely_ _ignoring_ the x86 specific
'handler' member of struct exception_table_entry. This effectively broke
the sorting as entries will only partly be swapped now.

Fortunately, the x86 Kconfig selects BUILDTIME_EXTABLE_SORT, so the
exception table doesn't need to be sorted at runtime. However, in case
that ever changes, we better not break the exception table sorting just
because of that.

Fix this by providing a swap_ex_entry_fixup() macro that takes care of
the 'handler' member.

[1] https://lkml.org/lkml/2016/1/27/232

Signed-off-by: Mathias Krause <minipli@xxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
---
 arch/x86/include/asm/uaccess.h |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index a969ae607be8..b69b7bffb0e0 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -108,6 +108,14 @@ struct exception_table_entry {
 
 #define ARCH_HAS_RELATIVE_EXTABLE
 
+#define swap_ex_entry_fixup(a, b, tmp, delta)			\
+	do {							\
+		(a)->fixup = (b)->fixup + (delta);		\
+		(b)->fixup = (tmp).fixup - (delta);		\
+		(a)->handler = (b)->handler + (delta);		\
+		(b)->handler = (tmp).handler - (delta);		\
+	} while (0)
+
 extern int fixup_exception(struct pt_regs *regs, int trapnr);
 extern bool ex_has_fault_handler(unsigned long ip);
 extern int early_fixup_exception(unsigned long *ip);
-- 
1.7.10.4