[PATCH v2 61/63] powerpc: Split memset() to avoid multi-field overflow

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Instead of writing across a field boundary with memset(), move the call
to just the array, and an explicit zeroing of the prior field.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Qinglang Miao <redacted>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Hulk Robot <redacted>
Cc: Wang Wensheng <redacted>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Kees Cook <redacted>
Reviewed-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/lkml/87czqsnmw9.fsf@mpe.ellerman.id.au
---
 drivers/macintosh/smu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/macintosh/smu.c b/drivers/macintosh/smu.c
index 94fb63a7b357..59ce431da7ef 100644
--- a/drivers/macintosh/smu.c
+++ b/drivers/macintosh/smu.c

@@ -848,7 +848,8 @@ int smu_queue_i2c(struct smu_i2c_cmd *cmd)
 	cmd->read = cmd->info.devaddr & 0x01;
 	switch(cmd->info.type) {
 	case SMU_I2C_TRANSFER_SIMPLE:
-		memset(&cmd->info.sublen, 0, 4);
+		cmd->info.sublen = 0;
+		memset(&cmd->info.subaddr, 0, 3);
 		break;
 	case SMU_I2C_TRANSFER_COMBINED:
 		cmd->info.devaddr &= 0xfe;

-- 
2.30.2

Le 18/08/2021 à 08:05, Kees Cook a écrit :

subaddr[] is a table, should the & be avoided ?
And while at it, why not use sizeof(subaddr) instead of 3 ?

  		break;
  	case SMU_I2C_TRANSFER_COMBINED:
  		cmd->info.devaddr &= 0xfe;

On Wed, Aug 18, 2021 at 08:42:18AM +0200, Christophe Leroy wrote:

Le 18/08/2021 à 08:05, Kees Cook a écrit :

quoted

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Instead of writing across a field boundary with memset(), move the call
to just the array, and an explicit zeroing of the prior field.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Qinglang Miao <redacted>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Hulk Robot <redacted>
Cc: Wang Wensheng <redacted>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Kees Cook <redacted>
Reviewed-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/lkml/87czqsnmw9.fsf@mpe.ellerman.id.au
---
  drivers/macintosh/smu.c | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/macintosh/smu.c b/drivers/macintosh/smu.c
index 94fb63a7b357..59ce431da7ef 100644
--- a/drivers/macintosh/smu.c
+++ b/drivers/macintosh/smu.c

@@ -848,7 +848,8 @@ int smu_queue_i2c(struct smu_i2c_cmd *cmd)
  	cmd->read = cmd->info.devaddr & 0x01;
  	switch(cmd->info.type) {
  	case SMU_I2C_TRANSFER_SIMPLE:
-		memset(&cmd->info.sublen, 0, 4);
+		cmd->info.sublen = 0;
+		memset(&cmd->info.subaddr, 0, 3);

subaddr[] is a table, should the & be avoided ?

It results in the same thing, but it's better form to not have the &; I
will fix this.

And while at it, why not use sizeof(subaddr) instead of 3 ?

Agreed. :)

Thanks!

-- 
Kees Cook