This is a note to let you know that I've just added the patch titled
bpf, x86: Fix tail call count offset calculation on bpf2bpf call
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bpf-x86-fix-tail-call-count-offset-calculation-on-bp.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 80478f4a984047eeeefe6bff903e76bd1f83fc76
Author: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
Date: Thu Jun 16 18:20:36 2022 +0200
bpf, x86: Fix tail call count offset calculation on bpf2bpf call
[ Upstream commit ff672c67ee7635ca1e28fb13729e8ef0d1f08ce5 ]
On x86-64 the tail call count is passed from one BPF function to another
through %rax. Additionally, on function entry, the tail call count value
is stored on stack right after the BPF program stack, due to register
shortage.
The stored count is later loaded from stack either when performing a tail
call - to check if we have not reached the tail call limit - or before
calling another BPF function call in order to pass it via %rax.
In the latter case, we miscalculate the offset at which the tail call count
was stored on function entry. The JIT does not take into account that the
allocated BPF program stack is always a multiple of 8 on x86, while the
actual stack depth does not have to be.
This leads to a load from an offset that belongs to the BPF stack, as shown
in the example below:
SEC("tc")
int entry(struct __sk_buff *skb)
{
/* Have data on stack which size is not a multiple of 8 */
volatile char arr[1] = {};
return subprog_tail(skb);
}
int entry(struct __sk_buff * skb):
0: (b4) w2 = 0
1: (73) *(u8 *)(r10 -1) = r2
2: (85) call pc+1#bpf_prog_ce2f79bb5f3e06dd_F
3: (95) exit
int entry(struct __sk_buff * skb):
0xffffffffa0201788: nop DWORD PTR [rax+rax*1+0x0]
0xffffffffa020178d: xor eax,eax
0xffffffffa020178f: push rbp
0xffffffffa0201790: mov rbp,rsp
0xffffffffa0201793: sub rsp,0x8
0xffffffffa020179a: push rax
0xffffffffa020179b: xor esi,esi
0xffffffffa020179d: mov BYTE PTR [rbp-0x1],sil
0xffffffffa02017a1: mov rax,QWORD PTR [rbp-0x9] !!! tail call count
0xffffffffa02017a8: call 0xffffffffa02017d8 !!! is at rbp-0x10
0xffffffffa02017ad: leave
0xffffffffa02017ae: ret
Fix it by rounding up the BPF stack depth to a multiple of 8, when
calculating the tail call count offset on stack.
Fixes: ebf7d1f508a7 ("bpf, x64: rework pro/epilogue and tailcall handling in JIT")
Signed-off-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx>
Acked-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20220616162037.535469-2-jakub@xxxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index d99434dc215c..8dca2bcbb0ea 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1440,8 +1440,9 @@ st: if (is_imm8(insn->off))
case BPF_JMP | BPF_CALL:
func = (u8 *) __bpf_call_base + imm32;
if (tail_call_reachable) {
+ /* mov rax, qword ptr [rbp - rounded_stack_depth - 8] */
EMIT3_off32(0x48, 0x8B, 0x85,
- -(bpf_prog->aux->stack_depth + 8));
+ -round_up(bpf_prog->aux->stack_depth, 8) - 8);
if (!imm32 || emit_call(&prog, func, image + addrs[i - 1] + 7))
return -EINVAL;
} else {
