diff mbox series

[bpf-next,v5,1/3] bpf: add some comments to stack representation

Message ID 20231208032519.260451-2-andreimatei1@gmail.com (mailing list archive)
State Accepted
Commit 92e1567ee3e3f6f160e320890ac77eec50bf8e7d
Delegated to: BPF
Headers show
Series bpf: fix accesses to uninit stack slots | expand

Checks

Context Check Description
bpf/vmtest-bpf-PR fail merge-conflict
netdev/tree_selection success Clearly marked for bpf
netdev/apply fail Patch does not apply to bpf

Commit Message

Andrei Matei Dec. 8, 2023, 3:25 a.m. UTC 
Add comments to the datastructure tracking the stack state, as the
mapping between each stack slot and where its state is stored is not
entirely obvious.

Signed-off-by: Andrei Matei <andreimatei1@gmail.com>
---
 include/linux/bpf_verifier.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

Comments

Eduard Zingerman Dec. 8, 2023, 9:06 p.m. UTC | #1 
On Thu, 2023-12-07 at 22:25 -0500, Andrei Matei wrote:
> Add comments to the datastructure tracking the stack state, as the
> mapping between each stack slot and where its state is stored is not
> entirely obvious.
> 
> Signed-off-by: Andrei Matei <andreimatei1@gmail.com>

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

Patch

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index bada59812e00..314b679fb494 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -321,7 +321,17 @@  struct bpf_func_state {
 	/* The following fields should be last. See copy_func_state() */
 	int acquired_refs;
 	struct bpf_reference_state *refs;
+	/* The state of the stack. Each element of the array describes BPF_REG_SIZE
+	 * (i.e. 8) bytes worth of stack memory.
+	 * stack[0] represents bytes [*(r10-8)..*(r10-1)]
+	 * stack[1] represents bytes [*(r10-16)..*(r10-9)]
+	 * ...
+	 * stack[allocated_stack/8 - 1] represents [*(r10-allocated_stack)..*(r10-allocated_stack+7)]
+	 */
 	struct bpf_stack_state *stack;
+	/* Size of the current stack, in bytes. The stack state is tracked below, in
+	 * `stack`. allocated_stack is always a multiple of BPF_REG_SIZE.
+	 */
 	int allocated_stack;
 };
 
@@ -658,6 +668,10 @@  struct bpf_verifier_env {
 	int exception_callback_subprog;
 	bool explore_alu_limits;
 	bool allow_ptr_leaks;
+	/* Allow access to uninitialized stack memory. Writes with fixed offset are
+	 * always allowed, so this refers to reads (with fixed or variable offset),
+	 * to writes with variable offset and to indirect (helper) accesses.
+	 */
 	bool allow_uninit_stack;
 	bool bpf_capable;
 	bool bypass_spec_v1;