FAILED: patch "[PATCH] bpf: Do not reject when the stack read size is different from" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Possible dependencies:

f30d4968e9ae ("bpf: Do not reject when the stack read size is different from the tracked scalar size") 354e8f1970f8 ("bpf: Support <8-byte scalar spill and refill")
27113c59b6d0 ("bpf: Check the other end of slot_type for STACK_SPILL")
2039f26f3aca ("bpf: Fix leakage due to insufficient speculative store bypass mitigation") 01f810ace9ed ("bpf: Allow variable-offset stack access")
cd17d38f8b28 ("bpf: Permits pointers on stack for helper calls")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f30d4968e9aee737e174fc97942af46cfb49b484 Mon Sep 17 00:00:00 2001
From: Martin KaFai Lau <[email protected]>
Date: Mon, 1 Nov 2021 23:45:35 -0700
Subject: [PATCH] bpf: Do not reject when the stack read size is different from
the tracked scalar size

Below is a simplified case from a report in bcc [0]:

r4 = 20
*(u32 *)(r10 -4) = r4
*(u32 *)(r10 -8) = r4 /* r4 state is tracked */
r4 = *(u64 *)(r10 -8) /* Read more than the tracked 32bit scalar.

			  * verifier rejects as 'corrupted spill memory'.
			  */

After commit 354e8f1970f8 ("bpf: Support <8-byte scalar spill and refill"), the 8-byte aligned 32bit spill is also tracked by the verifier and the register state is stored.

However, if 8 bytes are read from the stack instead of the tracked 4 byte scalar, then verifier currently rejects the program as "corrupted spill memory". This patch fixes this case by allowing it to read but marks the register as unknown.

Also note that, if the prog is trying to corrupt/leak an earlier spilled pointer by spilling another <8 bytes register on top, this has already been rejected in the check_stack_write_fixed_off().

[0] https://github.com/iovisor/bcc/pull/3683

index f0dca726ebfd..5f8d9128860a 100644
@@ -3088,9 +3088,12 @@ static int check_stack_read_fixed_off(struct bpf_verifier_env *env,
 	reg = &reg_state->stack[spi].spilled_ptr;
 
 	if (is_spilled_reg(&reg_state->stack[spi])) {
-		if (size != BPF_REG_SIZE) {
-			u8 scalar_size = 0;
+		u8 spill_size = 1;
+
+		for (i = BPF_REG_SIZE - 1; i > 0 && stype[i - 1] == STACK_SPILL; i--)
+			spill_size++;
 
+		if (size != BPF_REG_SIZE || spill_size != BPF_REG_SIZE) {
 			if (reg->type != SCALAR_VALUE) {
 				verbose_linfo(env, env->insn_idx, "; ");
 				verbose(env, "invalid size of register fill\n");

@@ -3101,10 +3104,7 @@ static int check_stack_read_fixed_off(struct bpf_verifier_env *env,
 			if (dst_regno < 0)
 				return 0;
 
-			for (i = BPF_REG_SIZE; i > 0 && stype[i - 1] == STACK_SPILL; i--)
-				scalar_size++;
-
-			if (!(off % BPF_REG_SIZE) && size == scalar_size) {
+			if (!(off % BPF_REG_SIZE) && size == spill_size) {
 				/* The earlier check_reg_arg() has decided the
 				 * subreg_def for this insn.  Save it first.
 				 */

@@ -3128,12 +3128,6 @@ static int check_stack_read_fixed_off(struct bpf_verifier_env *env,
 			state->regs[dst_regno].live |= REG_LIVE_WRITTEN;
 			return 0;
 		}
-		for (i = 1; i < BPF_REG_SIZE; i++) {
-			if (stype[(slot - i) % BPF_REG_SIZE] != STACK_SPILL) {
-				verbose(env, "corrupted spill memory\n");
-				return -EACCES;
-			}
-		}
 
 		if (dst_regno >= 0) {
 			/* restore register state from stack */