diff mbox series

[bpf-next,04/15] bpf: Make bpf_for_each_spilled_reg consider narrow spills

Message ID 20231220214013.3327288-5-maxtram95@gmail.com (mailing list archive)
State New, archived
Delegated to: BPF
Headers show
Series Improvements for tracking scalars in the BPF verifier | expand

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Commit Message

Maxim Mikityanskiy Dec. 20, 2023, 9:40 p.m. UTC 
From: Maxim Mikityanskiy <maxim@isovalent.com>

Adjust the check in bpf_get_spilled_reg to take into account spilled
registers narrower than 64 bits. That allows find_equal_scalars to
properly adjust the range of all spilled registers that have the same
ID. Before this change, it was possible for a register and a spilled
register to have the same IDs but different ranges if the spill was
narrower than 64 bits and a range check was performed on the register.

Signed-off-by: Maxim Mikityanskiy <maxim@isovalent.com>
---
 include/linux/bpf_verifier.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Eduard Zingerman Jan. 4, 2024, 2:25 a.m. UTC | #1 
On Wed, 2023-12-20 at 23:40 +0200, Maxim Mikityanskiy wrote:
> > From: Maxim Mikityanskiy <maxim@isovalent.com>
> > 
> > Adjust the check in bpf_get_spilled_reg to take into account spilled
> > registers narrower than 64 bits. That allows find_equal_scalars to
> > properly adjust the range of all spilled registers that have the same
> > ID. Before this change, it was possible for a register and a spilled
> > register to have the same IDs but different ranges if the spill was
> > narrower than 64 bits and a range check was performed on the register.
> > 
> > Signed-off-by: Maxim Mikityanskiy <maxim@isovalent.com>
> > ---

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

I double checked, all uses of bpf_for_each_reg_in_vstate() except
in find_equal_scalars() operate on 64-bit values (pointers),
so this change is ok.
diff mbox series

Patch

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index d07d857ca67f..e11baecbde68 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -453,7 +453,7 @@  struct bpf_verifier_state {
 
 #define bpf_get_spilled_reg(slot, frame, mask)				\
 	(((slot < frame->allocated_stack / BPF_REG_SIZE) &&		\
-	  ((1 << frame->stack[slot].slot_type[0]) & (mask))) \
+	  ((1 << frame->stack[slot].slot_type[BPF_REG_SIZE - 1]) & (mask))) \
 	 ? &frame->stack[slot].spilled_ptr : NULL)
 
 /* Iterate over 'frame', setting 'reg' to either NULL or a spilled register. */