From: Alexei Starovoitov ast@kernel.org
[ Upstream commit fe8d9571dc50232b569242fac7ea6332a654f186 ]
Since commit 177366bf7ceb the %rbp stopped pointing to %rbp of the previous stack frame. That broke frame pointer based stack unwinding. This commit is a partial revert of it. Note that the location of tail_call_cnt is fixed, since the verifier enforces MAX_BPF_STACK stack size for programs with tail calls.
Fixes: 177366bf7ceb ("bpf: change x86 JITed program stack layout") Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/net/bpf_jit_comp.c | 74 +++++++++++-------------------------- 1 file changed, 21 insertions(+), 53 deletions(-)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index afabf597c855..d88bc0935886 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -190,9 +190,7 @@ struct jit_context { #define BPF_MAX_INSN_SIZE 128 #define BPF_INSN_SAFETY 64
-#define AUX_STACK_SPACE 40 /* Space for RBX, R13, R14, R15, tailcnt */ - -#define PROLOGUE_SIZE 37 +#define PROLOGUE_SIZE 20
/* * Emit x86-64 prologue code for BPF program and check its size. @@ -203,44 +201,19 @@ static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf) u8 *prog = *pprog; int cnt = 0;
- /* push rbp */ - EMIT1(0x55); - - /* mov rbp,rsp */ - EMIT3(0x48, 0x89, 0xE5); - - /* sub rsp, rounded_stack_depth + AUX_STACK_SPACE */ - EMIT3_off32(0x48, 0x81, 0xEC, - round_up(stack_depth, 8) + AUX_STACK_SPACE); - - /* sub rbp, AUX_STACK_SPACE */ - EMIT4(0x48, 0x83, 0xED, AUX_STACK_SPACE); - - /* mov qword ptr [rbp+0],rbx */ - EMIT4(0x48, 0x89, 0x5D, 0); - /* mov qword ptr [rbp+8],r13 */ - EMIT4(0x4C, 0x89, 0x6D, 8); - /* mov qword ptr [rbp+16],r14 */ - EMIT4(0x4C, 0x89, 0x75, 16); - /* mov qword ptr [rbp+24],r15 */ - EMIT4(0x4C, 0x89, 0x7D, 24); - + EMIT1(0x55); /* push rbp */ + EMIT3(0x48, 0x89, 0xE5); /* mov rbp, rsp */ + /* sub rsp, rounded_stack_depth */ + EMIT3_off32(0x48, 0x81, 0xEC, round_up(stack_depth, 8)); + EMIT1(0x53); /* push rbx */ + EMIT2(0x41, 0x55); /* push r13 */ + EMIT2(0x41, 0x56); /* push r14 */ + EMIT2(0x41, 0x57); /* push r15 */ if (!ebpf_from_cbpf) { - /* - * Clear the tail call counter (tail_call_cnt): for eBPF tail - * calls we need to reset the counter to 0. It's done in two - * instructions, resetting RAX register to 0, and moving it - * to the counter location. - */ - - /* xor eax, eax */ - EMIT2(0x31, 0xc0); - /* mov qword ptr [rbp+32], rax */ - EMIT4(0x48, 0x89, 0x45, 32); - + /* zero init tail_call_cnt */ + EMIT2(0x6a, 0x00); BUILD_BUG_ON(cnt != PROLOGUE_SIZE); } - *pprog = prog; }
@@ -285,13 +258,13 @@ static void emit_bpf_tail_call(u8 **pprog) * if (tail_call_cnt > MAX_TAIL_CALL_CNT) * goto out; */ - EMIT2_off32(0x8B, 0x85, 36); /* mov eax, dword ptr [rbp + 36] */ + EMIT2_off32(0x8B, 0x85, -36 - MAX_BPF_STACK); /* mov eax, dword ptr [rbp - 548] */ EMIT3(0x83, 0xF8, MAX_TAIL_CALL_CNT); /* cmp eax, MAX_TAIL_CALL_CNT */ #define OFFSET2 (30 + RETPOLINE_RAX_BPF_JIT_SIZE) EMIT2(X86_JA, OFFSET2); /* ja out */ label2 = cnt; EMIT3(0x83, 0xC0, 0x01); /* add eax, 1 */ - EMIT2_off32(0x89, 0x85, 36); /* mov dword ptr [rbp + 36], eax */ + EMIT2_off32(0x89, 0x85, -36 - MAX_BPF_STACK); /* mov dword ptr [rbp -548], eax */
/* prog = array->ptrs[index]; */ EMIT4_off32(0x48, 0x8B, 0x84, 0xD6, /* mov rax, [rsi + rdx * 8 + offsetof(...)] */ @@ -1040,19 +1013,14 @@ xadd: if (is_imm8(insn->off)) seen_exit = true; /* Update cleanup_addr */ ctx->cleanup_addr = proglen; - /* mov rbx, qword ptr [rbp+0] */ - EMIT4(0x48, 0x8B, 0x5D, 0); - /* mov r13, qword ptr [rbp+8] */ - EMIT4(0x4C, 0x8B, 0x6D, 8); - /* mov r14, qword ptr [rbp+16] */ - EMIT4(0x4C, 0x8B, 0x75, 16); - /* mov r15, qword ptr [rbp+24] */ - EMIT4(0x4C, 0x8B, 0x7D, 24); - - /* add rbp, AUX_STACK_SPACE */ - EMIT4(0x48, 0x83, 0xC5, AUX_STACK_SPACE); - EMIT1(0xC9); /* leave */ - EMIT1(0xC3); /* ret */ + if (!bpf_prog_was_classic(bpf_prog)) + EMIT1(0x5B); /* get rid of tail_call_cnt */ + EMIT2(0x41, 0x5F); /* pop r15 */ + EMIT2(0x41, 0x5E); /* pop r14 */ + EMIT2(0x41, 0x5D); /* pop r13 */ + EMIT1(0x5B); /* pop rbx */ + EMIT1(0xC9); /* leave */ + EMIT1(0xC3); /* ret */ break;
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