From: Andrei Matei <andreimatei1@gmail.com>
Date: Thu, 7 Dec 2023 22:25:17 -0500
Subject: bpf: Add some comments to stack representation
Patch-mainline: v6.8-rc1
Git-commit: 92e1567ee3e3f6f160e320890ac77eec50bf8e7d
References: bsc#1220257 CVE-2023-52452

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>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20231208032519.260451-2-andreimatei1@gmail.com
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 include/linux/bpf_verifier.h |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -304,7 +304,17 @@ struct bpf_func_state {
 	/* The following fields should be last. See copy_func_state() */
 	int acquired_refs;
 	struct bpf_reference_state *refs;
+	/* 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;
+	/* 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;
 };
 
@@ -589,6 +599,10 @@ struct bpf_verifier_env {
 	u32 id_gen;			/* used to generate unique reg IDs */
 	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;