This is a note to let you know that I've just added the patch titled
bpf, arm64: Fix BTI type used for freplace attached functions
to the 6.4-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-arm64-fix-bti-type-used-for-freplace-attached-fu.patch
and it can be found in the queue-6.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 69e2c18524955cd8fb89335a4ddf8186f4aab6ec
Author: Alexander Duyck <alexanderduyck@xxxxxx>
Date: Thu Jul 13 09:49:31 2023 -0700
bpf, arm64: Fix BTI type used for freplace attached functions
[ Upstream commit a3f25d614bc73b45e8f02adc6769876dfd16ca84 ]
When running an freplace attached bpf program on an arm64 system w were
seeing the following issue:
Unhandled 64-bit el1h sync exception on CPU47, ESR 0x0000000036000003 -- BTI
After a bit of work to track it down I determined that what appeared to be
happening is that the 'bti c' at the start of the program was somehow being
reached after a 'br' instruction. Further digging pointed me toward the
fact that the function was attached via freplace. This in turn led me to
build_plt which I believe is invoking the long jump which is triggering
this error.
To resolve it we can replace the 'bti c' with 'bti jc' and add a comment
explaining why this has to be modified as such.
Fixes: b2ad54e1533e ("bpf, arm64: Implement bpf_arch_text_poke() for arm64")
Signed-off-by: Alexander Duyck <alexanderduyck@xxxxxx>
Acked-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
Link: https://lore.kernel.org/r/168926677665.316237.9953845318337455525.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index b26da8efa616e..0ce5f13eabb1b 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -322,7 +322,13 @@ static int build_prologue(struct jit_ctx *ctx, bool ebpf_from_cbpf)
*
*/
- emit_bti(A64_BTI_C, ctx);
+ /* bpf function may be invoked by 3 instruction types:
+ * 1. bl, attached via freplace to bpf prog via short jump
+ * 2. br, attached via freplace to bpf prog via long jump
+ * 3. blr, working as a function pointer, used by emit_call.
+ * So BTI_JC should used here to support both br and blr.
+ */
+ emit_bti(A64_BTI_JC, ctx);
emit(A64_MOV(1, A64_R(9), A64_LR), ctx);
emit(A64_NOP, ctx);
