summaryrefslogtreecommitdiff
path: root/drivers/char
diff options
context:
space:
mode:
authorGustavo A. R. Silva <gustavo@embeddedor.com>2020-05-08 19:38:26 +0300
committerJarkko Sakkinen <jarkko.sakkinen@linux.intel.com>2020-05-22 18:50:12 +0300
commitab91c2a89f86be2898cee208d492816ec238b2cf (patch)
tree9308c13226506e119388d3b4adce115a140f67bb /drivers/char
parent8c872863b4400d0c8e31a2ac16389fcaaede5e3c (diff)
downloadlinux-ab91c2a89f86be2898cee208d492816ec238b2cf.tar.xz
tpm: eventlog: Replace zero-length array with flexible-array member
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. Also, the following issue shows up due to the flexible-array member having incomplete type[4]: drivers/char/tpm/eventlog/tpm2.c: In function ‘tpm2_bios_measurements_start’: drivers/char/tpm/eventlog/tpm2.c:54:46: error: invalid application of ‘sizeof’ to incomplete type ‘u8[]’ {aka ‘unsigned char[]’} 54 | size = sizeof(struct tcg_pcr_event) - sizeof(event_header->event) | ^ drivers/char/tpm/eventlog/tpm2.c: In function ‘tpm2_bios_measurements_next’: drivers/char/tpm/eventlog/tpm2.c:102:10: error: invalid application of ‘sizeof’ to incomplete type ‘u8[]’ {aka ‘unsigned char[]’} 102 | sizeof(event_header->event) + event_header->event_size; | ^ drivers/char/tpm/eventlog/tpm2.c: In function ‘tpm2_binary_bios_measurements_show’: drivers/char/tpm/eventlog/tpm2.c:140:10: error: invalid application of ‘sizeof’ to incomplete type ‘u8[]’ {aka ‘unsigned char[]’} 140 | sizeof(event_header->event) + event_header->event_size; | ^ scripts/Makefile.build:266: recipe for target 'drivers/char/tpm/eventlog/tpm2.o' failed make[3]: *** [drivers/char/tpm/eventlog/tpm2.o] Error 1 As mentioned above: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] As in "sizeof(event_header->event) always evaluated to 0, so removing it has no effect". Lastly, make use of the struct_size() helper to deal with the flexible array member and its host structure. This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") [4] https://github.com/KSPP/linux/issues/43 Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> Reviewed-by: Kees Cook <keescook@chromium.org> Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Diffstat (limited to 'drivers/char')
-rw-r--r--drivers/char/tpm/eventlog/tpm2.c12
1 files changed, 5 insertions, 7 deletions
diff --git a/drivers/char/tpm/eventlog/tpm2.c b/drivers/char/tpm/eventlog/tpm2.c
index e741b1157525..37a05800980c 100644
--- a/drivers/char/tpm/eventlog/tpm2.c
+++ b/drivers/char/tpm/eventlog/tpm2.c
@@ -51,8 +51,7 @@ static void *tpm2_bios_measurements_start(struct seq_file *m, loff_t *pos)
int i;
event_header = addr;
- size = sizeof(struct tcg_pcr_event) - sizeof(event_header->event)
- + event_header->event_size;
+ size = struct_size(event_header, event, event_header->event_size);
if (*pos == 0) {
if (addr + size < limit) {
@@ -98,8 +97,8 @@ static void *tpm2_bios_measurements_next(struct seq_file *m, void *v,
event_header = log->bios_event_log;
if (v == SEQ_START_TOKEN) {
- event_size = sizeof(struct tcg_pcr_event) -
- sizeof(event_header->event) + event_header->event_size;
+ event_size = struct_size(event_header, event,
+ event_header->event_size);
marker = event_header;
} else {
event = v;
@@ -136,9 +135,8 @@ static int tpm2_binary_bios_measurements_show(struct seq_file *m, void *v)
size_t size;
if (v == SEQ_START_TOKEN) {
- size = sizeof(struct tcg_pcr_event) -
- sizeof(event_header->event) + event_header->event_size;
-
+ size = struct_size(event_header, event,
+ event_header->event_size);
temp_ptr = event_header;
if (size > 0)