[PATCH 4.18 002/171] powerpc/64/module: REL32 relocation range check

[Greg Kroah-Hartman]

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nicholas Piggin <npiggin@xxxxxxxxx>

[ Upstream commit b851ba02a6f3075f0f99c60c4bc30a4af80cf428 ]

The recent module relocation overflow crash demonstrated that we
have no range checking on REL32 relative relocations. This patch
implements a basic check, the same kernel that previously oopsed
and rebooted now continues with some of these errors when loading
the module:

  module_64: x_tables: REL32 527703503449812 out of range!

Possibly other relocations (ADDR32, REL16, TOC16, etc.) should also have
overflow checks.

Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/powerpc/kernel/module_64.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -685,7 +685,14 @@ int apply_relocate_add(Elf64_Shdr *sechd
 
 		case R_PPC64_REL32:
 			/* 32 bits relative (used by relative exception tables) */
-			*(u32 *)location = value - (unsigned long)location;
+			/* Convert value to relative */
+			value -= (unsigned long)location;
+			if (value + 0x80000000 > 0xffffffff) {
+				pr_err("%s: REL32 %li out of range!\n",
+				       me->name, (long int)value);
+				return -ENOEXEC;
+			}
+			*(u32 *)location = value;
 			break;
 
 		case R_PPC64_TOCSAVE: