This is a note to let you know that I've just added the patch titled
bpf: Fix mask generation for 32-bit narrow loads of 64-bit fields
to the 6.3-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-fix-mask-generation-for-32-bit-narrow-loads-of-64-bit-fields.patch
and it can be found in the queue-6.3 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 0613d8ca9ab382caabe9ed2dceb429e9781e443f Mon Sep 17 00:00:00 2001
From: Will Deacon <will@xxxxxxxxxx>
Date: Thu, 18 May 2023 11:25:28 +0100
Subject: bpf: Fix mask generation for 32-bit narrow loads of 64-bit fields
From: Will Deacon <will@xxxxxxxxxx>
commit 0613d8ca9ab382caabe9ed2dceb429e9781e443f upstream.
A narrow load from a 64-bit context field results in a 64-bit load
followed potentially by a 64-bit right-shift and then a bitwise AND
operation to extract the relevant data.
In the case of a 32-bit access, an immediate mask of 0xffffffff is used
to construct a 64-bit BPP_AND operation which then sign-extends the mask
value and effectively acts as a glorified no-op. For example:
0: 61 10 00 00 00 00 00 00 r0 = *(u32 *)(r1 + 0)
results in the following code generation for a 64-bit field:
ldr x7, [x7] // 64-bit load
mov x10, #0xffffffffffffffff
and x7, x7, x10
Fix the mask generation so that narrow loads always perform a 32-bit AND
operation:
ldr x7, [x7] // 64-bit load
mov w10, #0xffffffff
and w7, w7, w10
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: John Fastabend <john.fastabend@xxxxxxxxx>
Cc: Krzesimir Nowak <krzesimir@xxxxxxxxxx>
Cc: Andrey Ignatov <rdna@xxxxxx>
Acked-by: Yonghong Song <yhs@xxxxxx>
Fixes: 31fd85816dbe ("bpf: permits narrower load from bpf program context fields")
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230518102528.1341-1-will@xxxxxxxxxx
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/bpf/verifier.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -16017,7 +16017,7 @@ static int convert_ctx_accesses(struct b
insn_buf[cnt++] = BPF_ALU64_IMM(BPF_RSH,
insn->dst_reg,
shift);
- insn_buf[cnt++] = BPF_ALU64_IMM(BPF_AND, insn->dst_reg,
+ insn_buf[cnt++] = BPF_ALU32_IMM(BPF_AND, insn->dst_reg,
(1ULL << size * 8) - 1);
}
}
Patches currently in stable-queue which might be from will@xxxxxxxxxx are
queue-6.3/bpf-fix-mask-generation-for-32-bit-narrow-loads-of-64-bit-fields.patch
