s390/bpf: Implement exceptions
Implement the following three pieces required from the JIT: - A "top-level" BPF prog (exception_boundary) must save all non-volatile registers, and not only the ones that it clobbers. - A "handler" BPF prog (exception_cb) must switch stack to that of exception_boundary, and restore the registers that exception_boundary saved. - arch_bpf_stack_walk() must unwind the stack and provide the results in a way that satisfies both bpf_throw() and exception_cb. Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/20240703005047.40915-3-iii@linux.ibm.com
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@ -31,6 +31,7 @@
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#include <asm/nospec-branch.h>
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#include <asm/set_memory.h>
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#include <asm/text-patching.h>
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#include <asm/unwind.h>
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#include "bpf_jit.h"
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struct bpf_jit {
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@ -62,6 +63,8 @@ struct bpf_jit {
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#define SEEN_FUNC BIT(2) /* calls C functions */
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#define SEEN_STACK (SEEN_FUNC | SEEN_MEM)
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#define NVREGS 0xffc0 /* %r6-%r15 */
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/*
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* s390 registers
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*/
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@ -572,8 +575,21 @@ static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp,
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}
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/* Tail calls have to skip above initialization */
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jit->tail_call_start = jit->prg;
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if (fp->aux->exception_cb) {
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/*
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* Switch stack, the new address is in the 2nd parameter.
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*
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* Arrange the restoration of %r6-%r15 in the epilogue.
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* Do not restore them now, the prog does not need them.
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*/
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/* lgr %r15,%r3 */
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EMIT4(0xb9040000, REG_15, REG_3);
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jit->seen_regs |= NVREGS;
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} else {
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/* Save registers */
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save_restore_regs(jit, REGS_SAVE, stack_depth, 0);
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save_restore_regs(jit, REGS_SAVE, stack_depth,
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fp->aux->exception_boundary ? NVREGS : 0);
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}
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/* Setup literal pool */
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if (is_first_pass(jit) || (jit->seen & SEEN_LITERAL)) {
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if (!is_first_pass(jit) &&
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@ -2909,3 +2925,38 @@ bool bpf_jit_supports_insn(struct bpf_insn *insn, bool in_arena)
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*/
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return true;
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}
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bool bpf_jit_supports_exceptions(void)
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{
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/*
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* Exceptions require unwinding support, which is always available,
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* because the kernel is always built with backchain.
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*/
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return true;
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}
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void arch_bpf_stack_walk(bool (*consume_fn)(void *, u64, u64, u64),
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void *cookie)
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{
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unsigned long addr, prev_addr = 0;
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struct unwind_state state;
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unwind_for_each_frame(&state, NULL, NULL, 0) {
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addr = unwind_get_return_address(&state);
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if (!addr)
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break;
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/*
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* addr is a return address and state.sp is the value of %r15
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* at this address. exception_cb needs %r15 at entry to the
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* function containing addr, so take the next state.sp.
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*
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* There is no bp, and the exception_cb prog does not need one
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* to perform a quasi-longjmp. The common code requires a
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* non-zero bp, so pass sp there as well.
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*/
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if (prev_addr && !consume_fn(cookie, prev_addr, state.sp,
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state.sp))
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break;
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prev_addr = addr;
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}
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}
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