[PATCH 4.4 63/88] bpf/verifier: Add spi variable to check_stack_write()

Greg Kroah-Hartman
2018-12-14T12:16:52Z

From: Ben Hutchings <ben.hutchings@codethink.co.uk>

Extracted from commit dc503a8ad984 "bpf/verifier: track liveness for
pruning".

Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/bpf/verifier.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -572,7 +572,7 @@ static bool is_spillable_regtype(enum bp
static int check_stack_write(struct verifier_state *state, int off, int size,
int value_regno)
{
- int i;
+ int i, spi = (MAX_BPF_STACK + off) / BPF_REG_SIZE;
/* caller checked that off % size == 0 and -MAX_BPF_STACK <= off < 0,
* so it's aligned access and [off, off + size) are within stack limits
*/
@@ -587,15 +587,13 @@ static int check_stack_write(struct veri
}

/* save register state */
- state->spilled_regs[(MAX_BPF_STACK + off) / BPF_REG_SIZE] =
- state->regs[value_regno];
+ state->spilled_regs[spi] = state->regs[value_regno];

for (i = 0; i < BPF_REG_SIZE; i++)
state->stack_slot_type[MAX_BPF_STACK + off + i] = STACK_SPILL;
} else {
/* regular write of data into stack */
- state->spilled_regs[(MAX_BPF_STACK + off) / BPF_REG_SIZE] =
- (struct reg_state) {};
+ state->spilled_regs[spi] = (struct reg_state) {};

for (i = 0; i < size; i++)
state->stack_slot_type[MAX_BPF_STACK + off + i] = STACK_MISC;