When functions called by the trampoline panic, the backtrace that is
printed stops at the trampoline, because the trampoline does not store
its caller's frame address (backchain) on stack; it also stores the
return address at a wrong location.
Store both the same way as is already done for the regular eBPF
programs.
Fixes: 528eb2cb87bc ("s390/bpf: Implement arch_prepare_bpf_trampoline()")
Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
---
arch/s390/net/bpf_jit_comp.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 8955bc80270a..082b913f214e 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -2205,6 +2205,7 @@ struct bpf_tramp_jit {
* func_addr's original caller
*/
int stack_size; /* Trampoline stack size */
+ int backchain_off; /* Offset of backchain */
int stack_args_off; /* Offset of stack arguments for calling
* func_addr, has to be at the top
*/
@@ -2225,9 +2226,10 @@ struct bpf_tramp_jit {
* for __bpf_prog_enter() return value and
* func_addr respectively
*/
- int r14_off; /* Offset of saved %r14 */
int run_ctx_off; /* Offset of struct bpf_tramp_run_ctx */
int tccnt_off; /* Offset of saved tailcall counter */
+ int r14_off; /* Offset of saved %r14, has to be at the
+ * bottom */
int do_fexit; /* do_fexit: label */
};
@@ -2386,8 +2388,12 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
* Calculate the stack layout.
*/
- /* Reserve STACK_FRAME_OVERHEAD bytes for the callees. */
+ /*
+ * Allocate STACK_FRAME_OVERHEAD bytes for the callees. As the s390x
+ * ABI requires, put our backchain at the end of the allocated memory.
+ */
tjit->stack_size = STACK_FRAME_OVERHEAD;
+ tjit->backchain_off = tjit->stack_size - sizeof(u64);
tjit->stack_args_off = alloc_stack(tjit, nr_stack_args * sizeof(u64));
tjit->reg_args_off = alloc_stack(tjit, nr_reg_args * sizeof(u64));
tjit->ip_off = alloc_stack(tjit, sizeof(u64));
@@ -2395,10 +2401,10 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
tjit->bpf_args_off = alloc_stack(tjit, nr_bpf_args * sizeof(u64));
tjit->retval_off = alloc_stack(tjit, sizeof(u64));
tjit->r7_r8_off = alloc_stack(tjit, 2 * sizeof(u64));
- tjit->r14_off = alloc_stack(tjit, sizeof(u64));
tjit->run_ctx_off = alloc_stack(tjit,
sizeof(struct bpf_tramp_run_ctx));
tjit->tccnt_off = alloc_stack(tjit, sizeof(u64));
+ tjit->r14_off = alloc_stack(tjit, sizeof(u64) * 2);
/*
* In accordance with the s390x ABI, the caller has allocated
* STACK_FRAME_OVERHEAD bytes for us. 8 of them contain the caller's
@@ -2407,8 +2413,13 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
tjit->stack_size -= STACK_FRAME_OVERHEAD - sizeof(u64);
tjit->orig_stack_args_off = tjit->stack_size + STACK_FRAME_OVERHEAD;
+ /* lgr %r1,%r15 */
+ EMIT4(0xb9040000, REG_1, REG_15);
/* aghi %r15,-stack_size */
EMIT4_IMM(0xa70b0000, REG_15, -tjit->stack_size);
+ /* stg %r1,backchain_off(%r15) */
+ EMIT6_DISP_LH(0xe3000000, 0x0024, REG_1, REG_0, REG_15,
+ tjit->backchain_off);
/* mvc tccnt_off(4,%r15),stack_size+STK_OFF_TCCNT(%r15) */
_EMIT6(0xd203f000 | tjit->tccnt_off,
0xf000 | (tjit->stack_size + STK_OFF_TCCNT));
--
2.41.0
