[PATCH 6/7] powerpc: Make feature-fixup tests fortify-safe

[Kees Cook]

From: Daniel Axtens <dja@xxxxxxxxxx>

Testing the fortified string functions[1] would cause a kernel
panic on boot in test_feature_fixups() due to a buffer overflow
in memcmp.

This boils down to things like this:

  extern unsigned int ftr_fixup_test1;
  extern unsigned int ftr_fixup_test1_orig;

  check(memcmp(&ftr_fixup_test1, &ftr_fixup_test1_orig, size) == 0);

We know that these are asm labels so it is safe to read up to
'size' bytes at those addresses.

However, because we have passed the address of a single unsigned
int to memcmp, the compiler believes the underlying object is in
fact a single unsigned int. So if size > sizeof(unsigned int),
there will be a panic at runtime.

We can fix this by changing the types: instead of calling the asm
labels unsigned ints, call them unsigned int[]s. Therefore the
size isn't incorrectly determined at compile time and we get a
regular unsafe memcmp and no panic.

[1] http://openwall.com/lists/kernel-hardening/2017/05/09/2

Suggested-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Daniel Micay <danielmicay@xxxxxxxxx>
Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx>
Tested-by: Andrew Donnellan <andrew.donnellan@xxxxxxxxxxx>
Reviewed-by: Andrew Donnellan <andrew.donnellan@xxxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 arch/powerpc/lib/feature-fixups.c | 180 +++++++++++++++++++-------------------
 1 file changed, 90 insertions(+), 90 deletions(-)

diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c
index f3917705c686..41cf5ae273cf 100644
--- a/arch/powerpc/lib/feature-fixups.c
+++ b/arch/powerpc/lib/feature-fixups.c
@@ -233,192 +233,192 @@ static long calc_offset(struct fixup_entry *entry, unsigned int *p)
 
 static void test_basic_patching(void)
 {
-	extern unsigned int ftr_fixup_test1;
-	extern unsigned int end_ftr_fixup_test1;
-	extern unsigned int ftr_fixup_test1_orig;
-	extern unsigned int ftr_fixup_test1_expected;
-	int size = &end_ftr_fixup_test1 - &ftr_fixup_test1;
+	extern unsigned int ftr_fixup_test1[];
+	extern unsigned int end_ftr_fixup_test1[];
+	extern unsigned int ftr_fixup_test1_orig[];
+	extern unsigned int ftr_fixup_test1_expected[];
+	int size = end_ftr_fixup_test1 - ftr_fixup_test1;
 
 	fixup.value = fixup.mask = 8;
-	fixup.start_off = calc_offset(&fixup, &ftr_fixup_test1 + 1);
-	fixup.end_off = calc_offset(&fixup, &ftr_fixup_test1 + 2);
+	fixup.start_off = calc_offset(&fixup, ftr_fixup_test1 + 1);
+	fixup.end_off = calc_offset(&fixup, ftr_fixup_test1 + 2);
 	fixup.alt_start_off = fixup.alt_end_off = 0;
 
 	/* Sanity check */
-	check(memcmp(&ftr_fixup_test1, &ftr_fixup_test1_orig, size) == 0);
+	check(memcmp(ftr_fixup_test1, ftr_fixup_test1_orig, size) == 0);
 
 	/* Check we don't patch if the value matches */
 	patch_feature_section(8, &fixup);
-	check(memcmp(&ftr_fixup_test1, &ftr_fixup_test1_orig, size) == 0);
+	check(memcmp(ftr_fixup_test1, ftr_fixup_test1_orig, size) == 0);
 
 	/* Check we do patch if the value doesn't match */
 	patch_feature_section(0, &fixup);
-	check(memcmp(&ftr_fixup_test1, &ftr_fixup_test1_expected, size) == 0);
+	check(memcmp(ftr_fixup_test1, ftr_fixup_test1_expected, size) == 0);
 
 	/* Check we do patch if the mask doesn't match */
-	memcpy(&ftr_fixup_test1, &ftr_fixup_test1_orig, size);
-	check(memcmp(&ftr_fixup_test1, &ftr_fixup_test1_orig, size) == 0);
+	memcpy(ftr_fixup_test1, ftr_fixup_test1_orig, size);
+	check(memcmp(ftr_fixup_test1, ftr_fixup_test1_orig, size) == 0);
 	patch_feature_section(~8, &fixup);
-	check(memcmp(&ftr_fixup_test1, &ftr_fixup_test1_expected, size) == 0);
+	check(memcmp(ftr_fixup_test1, ftr_fixup_test1_expected, size) == 0);
 }
 
 static void test_alternative_patching(void)
 {
-	extern unsigned int ftr_fixup_test2;
-	extern unsigned int end_ftr_fixup_test2;
-	extern unsigned int ftr_fixup_test2_orig;
-	extern unsigned int ftr_fixup_test2_alt;
-	extern unsigned int ftr_fixup_test2_expected;
-	int size = &end_ftr_fixup_test2 - &ftr_fixup_test2;
+	extern unsigned int ftr_fixup_test2[];
+	extern unsigned int end_ftr_fixup_test2[];
+	extern unsigned int ftr_fixup_test2_orig[];
+	extern unsigned int ftr_fixup_test2_alt[];
+	extern unsigned int ftr_fixup_test2_expected[];
+	int size = end_ftr_fixup_test2 - ftr_fixup_test2;
 
 	fixup.value = fixup.mask = 0xF;
-	fixup.start_off = calc_offset(&fixup, &ftr_fixup_test2 + 1);
-	fixup.end_off = calc_offset(&fixup, &ftr_fixup_test2 + 2);
-	fixup.alt_start_off = calc_offset(&fixup, &ftr_fixup_test2_alt);
-	fixup.alt_end_off = calc_offset(&fixup, &ftr_fixup_test2_alt + 1);
+	fixup.start_off = calc_offset(&fixup, ftr_fixup_test2 + 1);
+	fixup.end_off = calc_offset(&fixup, ftr_fixup_test2 + 2);
+	fixup.alt_start_off = calc_offset(&fixup, ftr_fixup_test2_alt);
+	fixup.alt_end_off = calc_offset(&fixup, ftr_fixup_test2_alt + 1);
 
 	/* Sanity check */
-	check(memcmp(&ftr_fixup_test2, &ftr_fixup_test2_orig, size) == 0);
+	check(memcmp(ftr_fixup_test2, ftr_fixup_test2_orig, size) == 0);
 
 	/* Check we don't patch if the value matches */
 	patch_feature_section(0xF, &fixup);
-	check(memcmp(&ftr_fixup_test2, &ftr_fixup_test2_orig, size) == 0);
+	check(memcmp(ftr_fixup_test2, ftr_fixup_test2_orig, size) == 0);
 
 	/* Check we do patch if the value doesn't match */
 	patch_feature_section(0, &fixup);
-	check(memcmp(&ftr_fixup_test2, &ftr_fixup_test2_expected, size) == 0);
+	check(memcmp(ftr_fixup_test2, ftr_fixup_test2_expected, size) == 0);
 
 	/* Check we do patch if the mask doesn't match */
-	memcpy(&ftr_fixup_test2, &ftr_fixup_test2_orig, size);
-	check(memcmp(&ftr_fixup_test2, &ftr_fixup_test2_orig, size) == 0);
+	memcpy(ftr_fixup_test2, ftr_fixup_test2_orig, size);
+	check(memcmp(ftr_fixup_test2, ftr_fixup_test2_orig, size) == 0);
 	patch_feature_section(~0xF, &fixup);
-	check(memcmp(&ftr_fixup_test2, &ftr_fixup_test2_expected, size) == 0);
+	check(memcmp(ftr_fixup_test2, ftr_fixup_test2_expected, size) == 0);
 }
 
 static void test_alternative_case_too_big(void)
 {
-	extern unsigned int ftr_fixup_test3;
-	extern unsigned int end_ftr_fixup_test3;
-	extern unsigned int ftr_fixup_test3_orig;
-	extern unsigned int ftr_fixup_test3_alt;
-	int size = &end_ftr_fixup_test3 - &ftr_fixup_test3;
+	extern unsigned int ftr_fixup_test3[];
+	extern unsigned int end_ftr_fixup_test3[];
+	extern unsigned int ftr_fixup_test3_orig[];
+	extern unsigned int ftr_fixup_test3_alt[];
+	int size = end_ftr_fixup_test3 - ftr_fixup_test3;
 
 	fixup.value = fixup.mask = 0xC;
-	fixup.start_off = calc_offset(&fixup, &ftr_fixup_test3 + 1);
-	fixup.end_off = calc_offset(&fixup, &ftr_fixup_test3 + 2);
-	fixup.alt_start_off = calc_offset(&fixup, &ftr_fixup_test3_alt);
-	fixup.alt_end_off = calc_offset(&fixup, &ftr_fixup_test3_alt + 2);
+	fixup.start_off = calc_offset(&fixup, ftr_fixup_test3 + 1);
+	fixup.end_off = calc_offset(&fixup, ftr_fixup_test3 + 2);
+	fixup.alt_start_off = calc_offset(&fixup, ftr_fixup_test3_alt);
+	fixup.alt_end_off = calc_offset(&fixup, ftr_fixup_test3_alt + 2);
 
 	/* Sanity check */
-	check(memcmp(&ftr_fixup_test3, &ftr_fixup_test3_orig, size) == 0);
+	check(memcmp(ftr_fixup_test3, ftr_fixup_test3_orig, size) == 0);
 
 	/* Expect nothing to be patched, and the error returned to us */
 	check(patch_feature_section(0xF, &fixup) == 1);
-	check(memcmp(&ftr_fixup_test3, &ftr_fixup_test3_orig, size) == 0);
+	check(memcmp(ftr_fixup_test3, ftr_fixup_test3_orig, size) == 0);
 	check(patch_feature_section(0, &fixup) == 1);
-	check(memcmp(&ftr_fixup_test3, &ftr_fixup_test3_orig, size) == 0);
+	check(memcmp(ftr_fixup_test3, ftr_fixup_test3_orig, size) == 0);
 	check(patch_feature_section(~0xF, &fixup) == 1);
-	check(memcmp(&ftr_fixup_test3, &ftr_fixup_test3_orig, size) == 0);
+	check(memcmp(ftr_fixup_test3, ftr_fixup_test3_orig, size) == 0);
 }
 
 static void test_alternative_case_too_small(void)
 {
-	extern unsigned int ftr_fixup_test4;
-	extern unsigned int end_ftr_fixup_test4;
-	extern unsigned int ftr_fixup_test4_orig;
-	extern unsigned int ftr_fixup_test4_alt;
-	extern unsigned int ftr_fixup_test4_expected;
-	int size = &end_ftr_fixup_test4 - &ftr_fixup_test4;
+	extern unsigned int ftr_fixup_test4[];
+	extern unsigned int end_ftr_fixup_test4[];
+	extern unsigned int ftr_fixup_test4_orig[];
+	extern unsigned int ftr_fixup_test4_alt[];
+	extern unsigned int ftr_fixup_test4_expected[];
+	int size = end_ftr_fixup_test4 - ftr_fixup_test4;
 	unsigned long flag;
 
 	/* Check a high-bit flag */
 	flag = 1UL << ((sizeof(unsigned long) - 1) * 8);
 	fixup.value = fixup.mask = flag;
-	fixup.start_off = calc_offset(&fixup, &ftr_fixup_test4 + 1);
-	fixup.end_off = calc_offset(&fixup, &ftr_fixup_test4 + 5);
-	fixup.alt_start_off = calc_offset(&fixup, &ftr_fixup_test4_alt);
-	fixup.alt_end_off = calc_offset(&fixup, &ftr_fixup_test4_alt + 2);
+	fixup.start_off = calc_offset(&fixup, ftr_fixup_test4 + 1);
+	fixup.end_off = calc_offset(&fixup, ftr_fixup_test4 + 5);
+	fixup.alt_start_off = calc_offset(&fixup, ftr_fixup_test4_alt);
+	fixup.alt_end_off = calc_offset(&fixup, ftr_fixup_test4_alt + 2);
 
 	/* Sanity check */
-	check(memcmp(&ftr_fixup_test4, &ftr_fixup_test4_orig, size) == 0);
+	check(memcmp(ftr_fixup_test4, ftr_fixup_test4_orig, size) == 0);
 
 	/* Check we don't patch if the value matches */
 	patch_feature_section(flag, &fixup);
-	check(memcmp(&ftr_fixup_test4, &ftr_fixup_test4_orig, size) == 0);
+	check(memcmp(ftr_fixup_test4, ftr_fixup_test4_orig, size) == 0);
 
 	/* Check we do patch if the value doesn't match */
 	patch_feature_section(0, &fixup);
-	check(memcmp(&ftr_fixup_test4, &ftr_fixup_test4_expected, size) == 0);
+	check(memcmp(ftr_fixup_test4, ftr_fixup_test4_expected, size) == 0);
 
 	/* Check we do patch if the mask doesn't match */
-	memcpy(&ftr_fixup_test4, &ftr_fixup_test4_orig, size);
-	check(memcmp(&ftr_fixup_test4, &ftr_fixup_test4_orig, size) == 0);
+	memcpy(ftr_fixup_test4, ftr_fixup_test4_orig, size);
+	check(memcmp(ftr_fixup_test4, ftr_fixup_test4_orig, size) == 0);
 	patch_feature_section(~flag, &fixup);
-	check(memcmp(&ftr_fixup_test4, &ftr_fixup_test4_expected, size) == 0);
+	check(memcmp(ftr_fixup_test4, ftr_fixup_test4_expected, size) == 0);
 }
 
 static void test_alternative_case_with_branch(void)
 {
-	extern unsigned int ftr_fixup_test5;
-	extern unsigned int end_ftr_fixup_test5;
-	extern unsigned int ftr_fixup_test5_expected;
-	int size = &end_ftr_fixup_test5 - &ftr_fixup_test5;
+	extern unsigned int ftr_fixup_test5[];
+	extern unsigned int end_ftr_fixup_test5[];
+	extern unsigned int ftr_fixup_test5_expected[];
+	int size = end_ftr_fixup_test5 - ftr_fixup_test5;
 
-	check(memcmp(&ftr_fixup_test5, &ftr_fixup_test5_expected, size) == 0);
+	check(memcmp(ftr_fixup_test5, ftr_fixup_test5_expected, size) == 0);
 }
 
 static void test_alternative_case_with_external_branch(void)
 {
-	extern unsigned int ftr_fixup_test6;
-	extern unsigned int end_ftr_fixup_test6;
-	extern unsigned int ftr_fixup_test6_expected;
-	int size = &end_ftr_fixup_test6 - &ftr_fixup_test6;
+	extern unsigned int ftr_fixup_test6[];
+	extern unsigned int end_ftr_fixup_test6[];
+	extern unsigned int ftr_fixup_test6_expected[];
+	int size = end_ftr_fixup_test6 - ftr_fixup_test6;
 
-	check(memcmp(&ftr_fixup_test6, &ftr_fixup_test6_expected, size) == 0);
+	check(memcmp(ftr_fixup_test6, ftr_fixup_test6_expected, size) == 0);
 }
 
 static void test_cpu_macros(void)
 {
-	extern u8 ftr_fixup_test_FTR_macros;
-	extern u8 ftr_fixup_test_FTR_macros_expected;
-	unsigned long size = &ftr_fixup_test_FTR_macros_expected -
-			     &ftr_fixup_test_FTR_macros;
+	extern u8 ftr_fixup_test_FTR_macros[];
+	extern u8 ftr_fixup_test_FTR_macros_expected[];
+	unsigned long size = ftr_fixup_test_FTR_macros_expected -
+			     ftr_fixup_test_FTR_macros;
 
 	/* The fixups have already been done for us during boot */
-	check(memcmp(&ftr_fixup_test_FTR_macros,
-		     &ftr_fixup_test_FTR_macros_expected, size) == 0);
+	check(memcmp(ftr_fixup_test_FTR_macros,
+		     ftr_fixup_test_FTR_macros_expected, size) == 0);
 }
 
 static void test_fw_macros(void)
 {
 #ifdef CONFIG_PPC64
-	extern u8 ftr_fixup_test_FW_FTR_macros;
-	extern u8 ftr_fixup_test_FW_FTR_macros_expected;
-	unsigned long size = &ftr_fixup_test_FW_FTR_macros_expected -
-			     &ftr_fixup_test_FW_FTR_macros;
+	extern u8 ftr_fixup_test_FW_FTR_macros[];
+	extern u8 ftr_fixup_test_FW_FTR_macros_expected[];
+	unsigned long size = ftr_fixup_test_FW_FTR_macros_expected -
+			     ftr_fixup_test_FW_FTR_macros;
 
 	/* The fixups have already been done for us during boot */
-	check(memcmp(&ftr_fixup_test_FW_FTR_macros,
-		     &ftr_fixup_test_FW_FTR_macros_expected, size) == 0);
+	check(memcmp(ftr_fixup_test_FW_FTR_macros,
+		     ftr_fixup_test_FW_FTR_macros_expected, size) == 0);
 #endif
 }
 
 static void test_lwsync_macros(void)
 {
-	extern u8 lwsync_fixup_test;
-	extern u8 end_lwsync_fixup_test;
-	extern u8 lwsync_fixup_test_expected_LWSYNC;
-	extern u8 lwsync_fixup_test_expected_SYNC;
-	unsigned long size = &end_lwsync_fixup_test -
-			     &lwsync_fixup_test;
+	extern u8 lwsync_fixup_test[];
+	extern u8 end_lwsync_fixup_test[];
+	extern u8 lwsync_fixup_test_expected_LWSYNC[];
+	extern u8 lwsync_fixup_test_expected_SYNC[];
+	unsigned long size = end_lwsync_fixup_test -
+			     lwsync_fixup_test;
 
 	/* The fixups have already been done for us during boot */
 	if (cur_cpu_spec->cpu_features & CPU_FTR_LWSYNC) {
-		check(memcmp(&lwsync_fixup_test,
-			     &lwsync_fixup_test_expected_LWSYNC, size) == 0);
+		check(memcmp(lwsync_fixup_test,
+			     lwsync_fixup_test_expected_LWSYNC, size) == 0);
 	} else {
-		check(memcmp(&lwsync_fixup_test,
-			     &lwsync_fixup_test_expected_SYNC, size) == 0);
+		check(memcmp(lwsync_fixup_test,
+			     lwsync_fixup_test_expected_SYNC, size) == 0);
 	}
 }
 
-- 
2.7.4