diff options
author | Gustavo A. R. Silva <gustavo@embeddedor.com> | 2020-05-08 18:38:26 +0200 |
---|---|---|
committer | Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> | 2020-05-22 17:50:12 +0200 |
commit | ab91c2a89f86be2898cee208d492816ec238b2cf (patch) | |
tree | 9308c13226506e119388d3b4adce115a140f67bb /drivers/char/tpm | |
parent | tpm/tpm_ftpm_tee: Use UUID API for exporting the UUID (diff) | |
download | linux-ab91c2a89f86be2898cee208d492816ec238b2cf.tar.xz linux-ab91c2a89f86be2898cee208d492816ec238b2cf.zip |
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/tpm')
-rw-r--r-- | drivers/char/tpm/eventlog/tpm2.c | 12 |
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) |