Commit fa7bd4b0 authored by Ilya Leoshkevich's avatar Ilya Leoshkevich Committed by Daniel Borkmann
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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: default avatarIlya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240703005047.40915-3-iii@linux.ibm.com
parent 7ba4f43e

arch/s390/net/bpf_jit_comp.c

+53 −2
Original line number Diff line number Diff line
@@ -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;

	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, 0);

		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;

	}

}