[PATCH v3 1/2] powerpc64/bpf: fix tail calls for PCREL addressing

[Hari Bathini]

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 at vger.kernel.org
Signed-off-by: Hari Bathini <hbathini at 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
 	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)
-- 
2.44.0