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s390/bpf: Implement exceptions

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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
This commit is contained in:
Ilya Leoshkevich 2024-07-03 02:48:48 +02:00 committed by Daniel Borkmann
parent 7ba4f43e16
commit fa7bd4b000
1 changed files with 53 additions and 2 deletions
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55
arch/s390/net/bpf_jit_comp.c
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@ -31,6 +31,7 @@
#include <asm/nospec-branch.h>
#include <asm/set_memory.h>
#include <asm/text-patching.h>
#include <asm/unwind.h>
#include "bpf_jit.h"
struct bpf_jit {
@ -62,6 +63,8 @@ struct bpf_jit {
#define SEEN_FUNC BIT(2) /* calls C functions */
#define SEEN_STACK (SEEN_FUNC | SEEN_MEM)
#define NVREGS 0xffc0 /* %r6-%r15 */
/*
* s390 registers
*/
@ -572,8 +575,21 @@ static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp,
}
/* Tail calls have to skip above initialization */
jit->tail_call_start = jit->prg;
/* Save registers */
save_restore_regs(jit, REGS_SAVE, stack_depth, 0);
if (fp->aux->exception_cb) {
/*
* Switch stack, the new address is in the 2nd parameter.
*
* Arrange the restoration of %r6-%r15 in the epilogue.
* Do not restore them now, the prog does not need them.
*/
/* lgr %r15,%r3 */
EMIT4(0xb9040000, REG_15, REG_3);
jit->seen_regs |= NVREGS;
} else {
/* Save registers */
save_restore_regs(jit, REGS_SAVE, stack_depth,
fp->aux->exception_boundary ? NVREGS : 0);
}
/* Setup literal pool */
if (is_first_pass(jit) || (jit->seen & SEEN_LITERAL)) {
if (!is_first_pass(jit) &&
@ -2909,3 +2925,38 @@ bool bpf_jit_supports_insn(struct bpf_insn *insn, bool in_arena)
*/
return true;
}
bool bpf_jit_supports_exceptions(void)
{
/*
* Exceptions require unwinding support, which is always available,
* because the kernel is always built with backchain.
*/
return true;
}
void arch_bpf_stack_walk(bool (*consume_fn)(void *, u64, u64, u64),
void *cookie)
{
unsigned long addr, prev_addr = 0;
struct unwind_state state;
unwind_for_each_frame(&state, NULL, NULL, 0) {
addr = unwind_get_return_address(&state);
if (!addr)
break;
/*
* addr is a return address and state.sp is the value of %r15
* at this address. exception_cb needs %r15 at entry to the
* function containing addr, so take the next state.sp.
*
* There is no bp, and the exception_cb prog does not need one
* to perform a quasi-longjmp. The common code requires a
* non-zero bp, so pass sp there as well.
*/
if (prev_addr && !consume_fn(cookie, prev_addr, state.sp,
state.sp))
break;
prev_addr = addr;
}
}