Le 02/04/2024 à 12:58, Hari Bathini a écrit :

With PCREL addressing, there is no kernel TOC. So, it is not setup in prologue when PCREL addressing is used. But the number of instructions to skip on a tail call was not adjusted accordingly. That resulted in not so obvious failures while using tailcalls. 'tailcalls' selftest crashed the system with the below call trace:

bpf_test_run+0xe8/0x3cc (unreliable) bpf_prog_test_run_skb+0x348/0x778 __sys_bpf+0xb04/0x2b00 sys_bpf+0x28/0x38 system_call_exception+0x168/0x340 system_call_vectored_common+0x15c/0x2ec

Fixes: 7e3a68be42e1 ("powerpc/64: vmlinux support building with PCREL addresing") Cc: stable@vger.kernel.org Signed-off-by: Hari Bathini hbathini@linux.ibm.com

---

• Changes in v3:

  • New patch to fix tailcall issues with PCREL addressing.

  arch/powerpc/net/bpf_jit_comp64.c | 2 ++ 1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c index 79f23974a320..7f62ac4b4e65 100644 --- a/arch/powerpc/net/bpf_jit_comp64.c +++ b/arch/powerpc/net/bpf_jit_comp64.c @@ -285,8 +285,10 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o int b2p_index = bpf_to_ppc(BPF_REG_3); int bpf_tailcall_prologue_size = 8; +#ifndef CONFIG_PPC_KERNEL_PCREL

Any reason for not using IS_ENABLED(CONFIG_PPC_KERNEL_PCREL) ?

if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2)) bpf_tailcall_prologue_size += 4; /* skip past the toc load */ +#endif /* * if (index >= array->map.max_entries)