Messages in this thread | | | Date | Tue, 22 Nov 2022 13:03:55 +0530 | From | "Naveen N. Rao" <> | Subject | Re: [PATCH] powerpc/bpf/32: Fix Oops on tail call tests |
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Christophe Leroy wrote: > test_bpf tail call tests end up as: > > test_bpf: #0 Tail call leaf jited:1 85 PASS > test_bpf: #1 Tail call 2 jited:1 111 PASS > test_bpf: #2 Tail call 3 jited:1 145 PASS > test_bpf: #3 Tail call 4 jited:1 170 PASS > test_bpf: #4 Tail call load/store leaf jited:1 190 PASS > test_bpf: #5 Tail call load/store jited:1 > BUG: Unable to handle kernel data access on write at 0xf1b4e000 > Faulting instruction address: 0xbe86b710 > Oops: Kernel access of bad area, sig: 11 [#1] > BE PAGE_SIZE=4K MMU=Hash PowerMac > Modules linked in: test_bpf(+) > CPU: 0 PID: 97 Comm: insmod Not tainted 6.1.0-rc4+ #195 > Hardware name: PowerMac3,1 750CL 0x87210 PowerMac > NIP: be86b710 LR: be857e88 CTR: be86b704 > REGS: f1b4df20 TRAP: 0300 Not tainted (6.1.0-rc4+) > MSR: 00009032 <EE,ME,IR,DR,RI> CR: 28008242 XER: 00000000 > DAR: f1b4e000 DSISR: 42000000 > GPR00: 00000001 f1b4dfe0 c11d2280 00000000 00000000 00000000 00000002 00000000 > GPR08: f1b4e000 be86b704 f1b4e000 00000000 00000000 100d816a f2440000 fe73baa8 > GPR16: f2458000 00000000 c1941ae4 f1fe2248 00000045 c0de0000 f2458030 00000000 > GPR24: 000003e8 0000000f f2458000 f1b4dc90 3e584b46 00000000 f24466a0 c1941a00 > NIP [be86b710] 0xbe86b710 > LR [be857e88] __run_one+0xec/0x264 [test_bpf] > Call Trace: > [f1b4dfe0] [00000002] 0x2 (unreliable) > Instruction dump: > XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX > XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX > ---[ end trace 0000000000000000 ]--- > > This is a tentative to write above the stack. The problem is encoutered > with tests added by commit 38608ee7b690 ("bpf, tests: Add load store > test case for tail call") > > This happens because tail call is done to a BPF prog with a different > stack_depth. At the time being, the stack is kept as is when the caller > tail calls its callee. But at exit, the callee restores the stack based > on its own properties. Therefore here, at each run, r1 is erroneously > increased by 32 - 16 = 16 bytes. > > This was done that way in order to pass the tail call count from caller > to callee through the stack. As powerpc32 doesn't have a red zone in > the stack, it was necessary the maintain the stack as is for the tail > call. But it was not anticipated that the BPF frame size could be > different. > > Let's take a new approach. Use register r0 to carry the tail call count > during the tail call, and save it into the stack at function entry if > required. That's a deviation from the ppc32 ABI, but after all the way > tail calls are implemented is already not in accordance with the ABI.
Can we pass the tail call count in r4 instead?
> > With the fix, tail call tests are now successfull: > > test_bpf: #0 Tail call leaf jited:1 53 PASS > test_bpf: #1 Tail call 2 jited:1 115 PASS > test_bpf: #2 Tail call 3 jited:1 154 PASS > test_bpf: #3 Tail call 4 jited:1 165 PASS > test_bpf: #4 Tail call load/store leaf jited:1 101 PASS > test_bpf: #5 Tail call load/store jited:1 141 PASS > test_bpf: #6 Tail call error path, max count reached jited:1 994 PASS > test_bpf: #7 Tail call count preserved across function calls jited:1 140975 PASS > test_bpf: #8 Tail call error path, NULL target jited:1 110 PASS > test_bpf: #9 Tail call error path, index out of range jited:1 69 PASS > test_bpf: test_tail_calls: Summary: 10 PASSED, 0 FAILED, [10/10 JIT'ed] > > Fixes: 51c66ad849a7 ("powerpc/bpf: Implement extended BPF on PPC32") > Cc: stable@vger.kernel.org > Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> > --- > arch/powerpc/net/bpf_jit_comp32.c | 25 +++++++++++-------------- > 1 file changed, 11 insertions(+), 14 deletions(-) > > diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c > index 43f1c76d48ce..97e75b8181ca 100644 > --- a/arch/powerpc/net/bpf_jit_comp32.c > +++ b/arch/powerpc/net/bpf_jit_comp32.c > @@ -115,21 +115,19 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx) > > /* First arg comes in as a 32 bits pointer. */ > EMIT(PPC_RAW_MR(bpf_to_ppc(BPF_REG_1), _R3)); > - EMIT(PPC_RAW_LI(bpf_to_ppc(BPF_REG_1) - 1, 0)); > + EMIT(PPC_RAW_LI(_R0, 0)); > + > +#define BPF_TAILCALL_PROLOGUE_SIZE 8 > + > EMIT(PPC_RAW_STWU(_R1, _R1, -BPF_PPC_STACKFRAME(ctx))); > > /* > - * Initialize tail_call_cnt in stack frame if we do tail calls. > - * Otherwise, put in NOPs so that it can be skipped when we are > - * invoked through a tail call. > + * Save tail_call_cnt in stack frame if we do tail calls. > */ > if (ctx->seen & SEEN_TAILCALL) > - EMIT(PPC_RAW_STW(bpf_to_ppc(BPF_REG_1) - 1, _R1, > - bpf_jit_stack_offsetof(ctx, BPF_PPC_TC))); > - else > - EMIT(PPC_RAW_NOP()); > + EMIT(PPC_RAW_STW(_R0, _R1, bpf_jit_stack_offsetof(ctx, BPF_PPC_TC))); > > -#define BPF_TAILCALL_PROLOGUE_SIZE 16 > + EMIT(PPC_RAW_LI(bpf_to_ppc(BPF_REG_1) - 1, 0)); > > /* > * We need a stack frame, but we don't necessarily need to > @@ -244,7 +242,6 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o > EMIT(PPC_RAW_RLWINM(_R3, b2p_index, 2, 0, 29)); > EMIT(PPC_RAW_ADD(_R3, _R3, b2p_bpf_array)); > EMIT(PPC_RAW_LWZ(_R3, _R3, offsetof(struct bpf_array, ptrs))); > - EMIT(PPC_RAW_STW(_R0, _R1, bpf_jit_stack_offsetof(ctx, BPF_PPC_TC))); > > /* > * if (prog == NULL) > @@ -257,20 +254,20 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o > EMIT(PPC_RAW_LWZ(_R3, _R3, offsetof(struct bpf_prog, bpf_func))); > > if (ctx->seen & SEEN_FUNC) > - EMIT(PPC_RAW_LWZ(_R0, _R1, BPF_PPC_STACKFRAME(ctx) + PPC_LR_STKOFF)); > + EMIT(PPC_RAW_LWZ(_R5, _R1, BPF_PPC_STACKFRAME(ctx) + PPC_LR_STKOFF)); > > EMIT(PPC_RAW_ADDIC(_R3, _R3, BPF_TAILCALL_PROLOGUE_SIZE)); > > if (ctx->seen & SEEN_FUNC) > - EMIT(PPC_RAW_MTLR(_R0)); > + EMIT(PPC_RAW_MTLR(_R5));
Should we explicitly zero-out _R5 after this?
You can move the above PPC_RAW_LWZ() and PPC_RAW_MTLR() instructions, as well as the ADDI below for r1 into bpf_jit_emit_common_epilogue() and not have to repeat those here.
- Naveen
> > EMIT(PPC_RAW_MTCTR(_R3)); > > - EMIT(PPC_RAW_MR(_R3, bpf_to_ppc(BPF_REG_1))); > - > /* tear restore NVRs, ... */ > bpf_jit_emit_common_epilogue(image, ctx); > > + EMIT(PPC_RAW_ADDI(_R1, _R1, BPF_PPC_STACKFRAME(ctx))); > + > EMIT(PPC_RAW_BCTR()); > > /* out: */ > -- > 2.38.1 > >
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