verifier_subprog_precision.c

// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */

#include <errno.h>
#include <string.h>
#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include "bpf_misc.h"

#define ARRAY_SIZE(x) (sizeof(x) / sizeof(x[0]))

int vals[] SEC(".data.vals") = {1, 2, 3, 4};

__naked __noinline __used
static unsigned long identity_subprog()
{
	/* the simplest *static* 64-bit identity function */
	asm volatile (
		"r0 = r1;"
		"exit;"
	);
}

__noinline __used
unsigned long global_identity_subprog(__u64 x)
{
	/* the simplest *global* 64-bit identity function */
	return x;
}

__naked __noinline __used
static unsigned long callback_subprog()
{
	/* the simplest callback function */
	asm volatile (
		"r0 = 0;"
		"exit;"
	);
}

SEC("?raw_tp")
__success __log_level(2)
__msg("7: (0f) r1 += r0")
__msg("mark_precise: frame0: regs=r0 stack= before 6: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r0 stack= before 5: (27) r0 *= 4")
__msg("mark_precise: frame0: regs=r0 stack= before 11: (95) exit")
__msg("mark_precise: frame1: regs=r0 stack= before 10: (bf) r0 = r1")
__msg("mark_precise: frame1: regs=r1 stack= before 4: (85) call pc+5")
__msg("mark_precise: frame0: regs=r1 stack= before 3: (bf) r1 = r6")
__msg("mark_precise: frame0: regs=r6 stack= before 2: (b7) r6 = 3")
__naked int subprog_result_precise(void)
{
	asm volatile (
		"r6 = 3;"
		/* pass r6 through r1 into subprog to get it back as r0;
		 * this whole chain will have to be marked as precise later
		 */
		"r1 = r6;"
		"call identity_subprog;"
		/* now use subprog's returned value (which is a
		 * r6 -> r1 -> r0 chain), as index into vals array, forcing
		 * all of that to be known precisely
		 */
		"r0 *= 4;"
		"r1 = %[vals];"
		/* here r0->r1->r6 chain is forced to be precise and has to be
		 * propagated back to the beginning, including through the
		 * subprog call
		 */
		"r1 += r0;"
		"r0 = *(u32 *)(r1 + 0);"
		"exit;"
		:
		: __imm_ptr(vals)
		: __clobber_common, "r6"
	);
}

SEC("?raw_tp")
__success __log_level(2)
__msg("9: (0f) r1 += r0")
__msg("mark_precise: frame0: last_idx 9 first_idx 0")
__msg("mark_precise: frame0: regs=r0 stack= before 8: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r0 stack= before 7: (27) r0 *= 4")
__msg("mark_precise: frame0: regs=r0 stack= before 5: (a5) if r0 < 0x4 goto pc+1")
__msg("mark_precise: frame0: regs=r0 stack= before 4: (85) call pc+7")
__naked int global_subprog_result_precise(void)
{
	asm volatile (
		"r6 = 3;"
		/* pass r6 through r1 into subprog to get it back as r0;
		 * given global_identity_subprog is global, precision won't
		 * propagate all the way back to r6
		 */
		"r1 = r6;"
		"call global_identity_subprog;"
		/* now use subprog's returned value (which is unknown now, so
		 * we need to clamp it), as index into vals array, forcing r0
		 * to be marked precise (with no effect on r6, though)
		 */
		"if r0 < %[vals_arr_sz] goto 1f;"
		"r0 = %[vals_arr_sz] - 1;"
	"1:"
		"r0 *= 4;"
		"r1 = %[vals];"
		/* here r0 is forced to be precise and has to be
		 * propagated back to the global subprog call, but it
		 * shouldn't go all the way to mark r6 as precise
		 */
		"r1 += r0;"
		"r0 = *(u32 *)(r1 + 0);"
		"exit;"
		:
		: __imm_ptr(vals),
		  __imm_const(vals_arr_sz, ARRAY_SIZE(vals))
		: __clobber_common, "r6"
	);
}

SEC("?raw_tp")
__success __log_level(2)
/* First simulated path does not include callback body,
 * r1 and r4 are always precise for bpf_loop() calls.
 */
__msg("9: (85) call bpf_loop#181")
__msg("mark_precise: frame0: last_idx 9 first_idx 9 subseq_idx -1")
__msg("mark_precise: frame0: parent state regs=r4 stack=:")
__msg("mark_precise: frame0: last_idx 8 first_idx 0 subseq_idx 9")
__msg("mark_precise: frame0: regs=r4 stack= before 8: (b7) r4 = 0")
__msg("mark_precise: frame0: last_idx 9 first_idx 9 subseq_idx -1")
__msg("mark_precise: frame0: parent state regs=r1 stack=:")
__msg("mark_precise: frame0: last_idx 8 first_idx 0 subseq_idx 9")
__msg("mark_precise: frame0: regs=r1 stack= before 8: (b7) r4 = 0")
__msg("mark_precise: frame0: regs=r1 stack= before 7: (b7) r3 = 0")
__msg("mark_precise: frame0: regs=r1 stack= before 6: (bf) r2 = r8")
__msg("mark_precise: frame0: regs=r1 stack= before 5: (bf) r1 = r6")
__msg("mark_precise: frame0: regs=r6 stack= before 4: (b7) r6 = 3")
/* r6 precision propagation */
__msg("14: (0f) r1 += r6")
__msg("mark_precise: frame0: last_idx 14 first_idx 9")
__msg("mark_precise: frame0: regs=r6 stack= before 13: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r6 stack= before 12: (27) r6 *= 4")
__msg("mark_precise: frame0: regs=r6 stack= before 11: (25) if r6 > 0x3 goto pc+4")
__msg("mark_precise: frame0: regs=r6 stack= before 10: (bf) r6 = r0")
__msg("mark_precise: frame0: regs=r0 stack= before 9: (85) call bpf_loop")
/* State entering callback body popped from states stack */
__msg("from 9 to 17: frame1:")
__msg("17: frame1: R1=scalar() R2=0 R10=fp0 cb")
__msg("17: (b7) r0 = 0")
__msg("18: (95) exit")
__msg("returning from callee:")
__msg("to caller at 9:")
__msg("frame 0: propagating r1,r4")
__msg("mark_precise: frame0: last_idx 9 first_idx 9 subseq_idx -1")
__msg("mark_precise: frame0: regs=r1,r4 stack= before 18: (95) exit")
__msg("from 18 to 9: safe")
__naked int callback_result_precise(void)
{
	asm volatile (
		"r6 = 3;"

		/* call subprog and use result; r0 shouldn't propagate back to
		 * callback_subprog
		 */
		"r1 = r6;"			/* nr_loops */
		"r2 = %[callback_subprog];"	/* callback_fn */
		"r3 = 0;"			/* callback_ctx */
		"r4 = 0;"			/* flags */
		"call %[bpf_loop];"

		"r6 = r0;"
		"if r6 > 3 goto 1f;"
		"r6 *= 4;"
		"r1 = %[vals];"
		/* here r6 is forced to be precise and has to be propagated
		 * back to the bpf_loop() call, but not beyond
		 */
		"r1 += r6;"
		"r0 = *(u32 *)(r1 + 0);"
	"1:"
		"exit;"
		:
		: __imm_ptr(vals),
		  __imm_ptr(callback_subprog),
		  __imm(bpf_loop)
		: __clobber_common, "r6"
	);
}

SEC("?raw_tp")
__success __log_level(2)
__msg("7: (0f) r1 += r6")
__msg("mark_precise: frame0: last_idx 7 first_idx 0")
__msg("mark_precise: frame0: regs=r6 stack= before 6: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r6 stack= before 5: (27) r6 *= 4")
__msg("mark_precise: frame0: regs=r6 stack= before 11: (95) exit")
__msg("mark_precise: frame1: regs= stack= before 10: (bf) r0 = r1")
__msg("mark_precise: frame1: regs= stack= before 4: (85) call pc+5")
__msg("mark_precise: frame0: regs=r6 stack= before 3: (b7) r1 = 0")
__msg("mark_precise: frame0: regs=r6 stack= before 2: (b7) r6 = 3")
__naked int parent_callee_saved_reg_precise(void)
{
	asm volatile (
		"r6 = 3;"

		/* call subprog and ignore result; we need this call only to
		 * complicate jump history
		 */
		"r1 = 0;"
		"call identity_subprog;"

		"r6 *= 4;"
		"r1 = %[vals];"
		/* here r6 is forced to be precise and has to be propagated
		 * back to the beginning, handling (and ignoring) subprog call
		 */
		"r1 += r6;"
		"r0 = *(u32 *)(r1 + 0);"
		"exit;"
		:
		: __imm_ptr(vals)
		: __clobber_common, "r6"
	);
}

SEC("?raw_tp")
__success __log_level(2)
__msg("7: (0f) r1 += r6")
__msg("mark_precise: frame0: last_idx 7 first_idx 0")
__msg("mark_precise: frame0: regs=r6 stack= before 6: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r6 stack= before 5: (27) r6 *= 4")
__msg("mark_precise: frame0: regs=r6 stack= before 4: (85) call pc+5")
__msg("mark_precise: frame0: regs=r6 stack= before 3: (b7) r1 = 0")
__msg("mark_precise: frame0: regs=r6 stack= before 2: (b7) r6 = 3")
__naked int parent_callee_saved_reg_precise_global(void)
{
	asm volatile (
		"r6 = 3;"

		/* call subprog and ignore result; we need this call only to
		 * complicate jump history
		 */
		"r1 = 0;"
		"call global_identity_subprog;"

		"r6 *= 4;"
		"r1 = %[vals];"
		/* here r6 is forced to be precise and has to be propagated
		 * back to the beginning, handling (and ignoring) subprog call
		 */
		"r1 += r6;"
		"r0 = *(u32 *)(r1 + 0);"
		"exit;"
		:
		: __imm_ptr(vals)
		: __clobber_common, "r6"
	);
}

SEC("?raw_tp")
__success __log_level(2)
/* First simulated path does not include callback body */
__msg("12: (0f) r1 += r6")
__msg("mark_precise: frame0: last_idx 12 first_idx 9")
__msg("mark_precise: frame0: regs=r6 stack= before 11: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r6 stack= before 10: (27) r6 *= 4")
__msg("mark_precise: frame0: regs=r6 stack= before 9: (85) call bpf_loop")
__msg("mark_precise: frame0: parent state regs=r6 stack=:")
__msg("mark_precise: frame0: last_idx 8 first_idx 0 subseq_idx 9")
__msg("mark_precise: frame0: regs=r6 stack= before 8: (b7) r4 = 0")
__msg("mark_precise: frame0: regs=r6 stack= before 7: (b7) r3 = 0")
__msg("mark_precise: frame0: regs=r6 stack= before 6: (bf) r2 = r8")
__msg("mark_precise: frame0: regs=r6 stack= before 5: (b7) r1 = 1")
__msg("mark_precise: frame0: regs=r6 stack= before 4: (b7) r6 = 3")
/* State entering callback body popped from states stack */
__msg("from 9 to 15: frame1:")
__msg("15: frame1: R1=scalar() R2=0 R10=fp0 cb")
__msg("15: (b7) r0 = 0")
__msg("16: (95) exit")
__msg("returning from callee:")
__msg("to caller at 9:")
/* r1, r4 are always precise for bpf_loop(),
 * r6 was marked before backtracking to callback body.
 */
__msg("frame 0: propagating r1,r4,r6")
__msg("mark_precise: frame0: last_idx 9 first_idx 9 subseq_idx -1")
__msg("mark_precise: frame0: regs=r1,r4,r6 stack= before 16: (95) exit")
__msg("mark_precise: frame1: regs= stack= before 15: (b7) r0 = 0")
__msg("mark_precise: frame1: regs= stack= before 9: (85) call bpf_loop")
__msg("mark_precise: frame0: parent state regs= stack=:")
__msg("from 16 to 9: safe")
__naked int parent_callee_saved_reg_precise_with_callback(void)
{
	asm volatile (
		"r6 = 3;"

		/* call subprog and ignore result; we need this call only to
		 * complicate jump history
		 */
		"r1 = 1;"			/* nr_loops */
		"r2 = %[callback_subprog];"	/* callback_fn */
		"r3 = 0;"			/* callback_ctx */
		"r4 = 0;"			/* flags */
		"call %[bpf_loop];"

		"r6 *= 4;"
		"r1 = %[vals];"
		/* here r6 is forced to be precise and has to be propagated
		 * back to the beginning, handling (and ignoring) callback call
		 */
		"r1 += r6;"
		"r0 = *(u32 *)(r1 + 0);"
		"exit;"
		:
		: __imm_ptr(vals),
		  __imm_ptr(callback_subprog),
		  __imm(bpf_loop)
		: __clobber_common, "r6"
	);
}

SEC("?raw_tp")
__success __log_level(2)
__msg("9: (0f) r1 += r6")
__msg("mark_precise: frame0: last_idx 9 first_idx 6")
__msg("mark_precise: frame0: regs=r6 stack= before 8: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r6 stack= before 7: (27) r6 *= 4")
__msg("mark_precise: frame0: regs=r6 stack= before 6: (79) r6 = *(u64 *)(r10 -8)")
__msg("mark_precise: frame0: parent state regs= stack=-8:")
__msg("mark_precise: frame0: last_idx 13 first_idx 0")
__msg("mark_precise: frame0: regs= stack=-8 before 13: (95) exit")
__msg("mark_precise: frame1: regs= stack= before 12: (bf) r0 = r1")
__msg("mark_precise: frame1: regs= stack= before 5: (85) call pc+6")
__msg("mark_precise: frame0: regs= stack=-8 before 4: (b7) r1 = 0")
__msg("mark_precise: frame0: regs= stack=-8 before 3: (7b) *(u64 *)(r10 -8) = r6")
__msg("mark_precise: frame0: regs=r6 stack= before 2: (b7) r6 = 3")
__naked int parent_stack_slot_precise(void)
{
	asm volatile (
		/* spill reg */
		"r6 = 3;"
		"*(u64 *)(r10 - 8) = r6;"

		/* call subprog and ignore result; we need this call only to
		 * complicate jump history
		 */
		"r1 = 0;"
		"call identity_subprog;"

		/* restore reg from stack; in this case we'll be carrying
		 * stack mask when going back into subprog through jump
		 * history
		 */
		"r6 = *(u64 *)(r10 - 8);"

		"r6 *= 4;"
		"r1 = %[vals];"
		/* here r6 is forced to be precise and has to be propagated
		 * back to the beginning, handling (and ignoring) subprog call
		 */
		"r1 += r6;"
		"r0 = *(u32 *)(r1 + 0);"
		"exit;"
		:
		: __imm_ptr(vals)
		: __clobber_common, "r6"
	);
}

SEC("?raw_tp")
__success __log_level(2)
__msg("9: (0f) r1 += r6")
__msg("mark_precise: frame0: last_idx 9 first_idx 6")
__msg("mark_precise: frame0: regs=r6 stack= before 8: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r6 stack= before 7: (27) r6 *= 4")
__msg("mark_precise: frame0: regs=r6 stack= before 6: (79) r6 = *(u64 *)(r10 -8)")
__msg("mark_precise: frame0: parent state regs= stack=-8:")
__msg("mark_precise: frame0: last_idx 5 first_idx 0")
__msg("mark_precise: frame0: regs= stack=-8 before 5: (85) call pc+6")
__msg("mark_precise: frame0: regs= stack=-8 before 4: (b7) r1 = 0")
__msg("mark_precise: frame0: regs= stack=-8 before 3: (7b) *(u64 *)(r10 -8) = r6")
__msg("mark_precise: frame0: regs=r6 stack= before 2: (b7) r6 = 3")
__naked int parent_stack_slot_precise_global(void)
{
	asm volatile (
		/* spill reg */
		"r6 = 3;"
		"*(u64 *)(r10 - 8) = r6;"

		/* call subprog and ignore result; we need this call only to
		 * complicate jump history
		 */
		"r1 = 0;"
		"call global_identity_subprog;"

		/* restore reg from stack; in this case we'll be carrying
		 * stack mask when going back into subprog through jump
		 * history
		 */
		"r6 = *(u64 *)(r10 - 8);"

		"r6 *= 4;"
		"r1 = %[vals];"
		/* here r6 is forced to be precise and has to be propagated
		 * back to the beginning, handling (and ignoring) subprog call
		 */
		"r1 += r6;"
		"r0 = *(u32 *)(r1 + 0);"
		"exit;"
		:
		: __imm_ptr(vals)
		: __clobber_common, "r6"
	);
}

SEC("?raw_tp")
__success __log_level(2)
/* First simulated path does not include callback body */
__msg("14: (0f) r1 += r6")
__msg("mark_precise: frame0: last_idx 14 first_idx 10")
__msg("mark_precise: frame0: regs=r6 stack= before 13: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r6 stack= before 12: (27) r6 *= 4")
__msg("mark_precise: frame0: regs=r6 stack= before 11: (79) r6 = *(u64 *)(r10 -8)")
__msg("mark_precise: frame0: regs= stack=-8 before 10: (85) call bpf_loop")
__msg("mark_precise: frame0: parent state regs= stack=-8:")
__msg("mark_precise: frame0: last_idx 9 first_idx 0 subseq_idx 10")
__msg("mark_precise: frame0: regs= stack=-8 before 9: (b7) r4 = 0")
__msg("mark_precise: frame0: regs= stack=-8 before 8: (b7) r3 = 0")
__msg("mark_precise: frame0: regs= stack=-8 before 7: (bf) r2 = r8")
__msg("mark_precise: frame0: regs= stack=-8 before 6: (bf) r1 = r6")
__msg("mark_precise: frame0: regs= stack=-8 before 5: (7b) *(u64 *)(r10 -8) = r6")
__msg("mark_precise: frame0: regs=r6 stack= before 4: (b7) r6 = 3")
/* State entering callback body popped from states stack */
__msg("from 10 to 17: frame1:")
__msg("17: frame1: R1=scalar() R2=0 R10=fp0 cb")
__msg("17: (b7) r0 = 0")
__msg("18: (95) exit")
__msg("returning from callee:")
__msg("to caller at 10:")
/* r1, r4 are always precise for bpf_loop(),
 * fp-8 was marked before backtracking to callback body.
 */
__msg("frame 0: propagating r1,r4,fp-8")
__msg("mark_precise: frame0: last_idx 10 first_idx 10 subseq_idx -1")
__msg("mark_precise: frame0: regs=r1,r4 stack=-8 before 18: (95) exit")
__msg("mark_precise: frame1: regs= stack= before 17: (b7) r0 = 0")
__msg("mark_precise: frame1: regs= stack= before 10: (85) call bpf_loop#181")
__msg("mark_precise: frame0: parent state regs= stack=:")
__msg("from 18 to 10: safe")
__naked int parent_stack_slot_precise_with_callback(void)
{
	asm volatile (
		/* spill reg */
		"r6 = 3;"
		"*(u64 *)(r10 - 8) = r6;"

		/* ensure we have callback frame in jump history */
		"r1 = r6;"			/* nr_loops */
		"r2 = %[callback_subprog];"	/* callback_fn */
		"r3 = 0;"			/* callback_ctx */
		"r4 = 0;"			/* flags */
		"call %[bpf_loop];"

		/* restore reg from stack; in this case we'll be carrying
		 * stack mask when going back into subprog through jump
		 * history
		 */
		"r6 = *(u64 *)(r10 - 8);"

		"r6 *= 4;"
		"r1 = %[vals];"
		/* here r6 is forced to be precise and has to be propagated
		 * back to the beginning, handling (and ignoring) subprog call
		 */
		"r1 += r6;"
		"r0 = *(u32 *)(r1 + 0);"
		"exit;"
		:
		: __imm_ptr(vals),
		  __imm_ptr(callback_subprog),
		  __imm(bpf_loop)
		: __clobber_common, "r6"
	);
}

__noinline __used
static __u64 subprog_with_precise_arg(__u64 x)
{
	return vals[x]; /* x is forced to be precise */
}

SEC("?raw_tp")
__success __log_level(2)
__msg("8: (0f) r2 += r1")
__msg("mark_precise: frame1: last_idx 8 first_idx 0")
__msg("mark_precise: frame1: regs=r1 stack= before 6: (18) r2 = ")
__msg("mark_precise: frame1: regs=r1 stack= before 5: (67) r1 <<= 2")
__msg("mark_precise: frame1: regs=r1 stack= before 2: (85) call pc+2")
__msg("mark_precise: frame0: regs=r1 stack= before 1: (bf) r1 = r6")
__msg("mark_precise: frame0: regs=r6 stack= before 0: (b7) r6 = 3")
__naked int subprog_arg_precise(void)
{
	asm volatile (
		"r6 = 3;"
		"r1 = r6;"
		/* subprog_with_precise_arg expects its argument to be
		 * precise, so r1->r6 will be marked precise from inside the
		 * subprog
		 */
		"call subprog_with_precise_arg;"
		"r0 += r6;"
		"exit;"
		:
		:
		: __clobber_common, "r6"
	);
}

/* r1 is pointer to stack slot;
 * r2 is a register to spill into that slot
 * subprog also spills r2 into its own stack slot
 */
__naked __noinline __used
static __u64 subprog_spill_reg_precise(void)
{
	asm volatile (
		/* spill to parent stack */
		"*(u64 *)(r1 + 0) = r2;"
		/* spill to subprog stack (we use -16 offset to avoid
		 * accidental confusion with parent's -8 stack slot in
		 * verifier log output)
		 */
		"*(u64 *)(r10 - 16) = r2;"
		/* use both spills as return result to propagete precision everywhere */
		"r0 = *(u64 *)(r10 - 16);"
		"r2 = *(u64 *)(r1 + 0);"
		"r0 += r2;"
		"exit;"
	);
}

SEC("?raw_tp")
__success __log_level(2)
/* precision backtracking can't currently handle stack access not through r10,
 * so we won't be able to mark stack slot fp-8 as precise, and so will
 * fallback to forcing all as precise
 */
__msg("mark_precise: frame0: falling back to forcing all scalars precise")
__naked int subprog_spill_into_parent_stack_slot_precise(void)
{
	asm volatile (
		"r6 = 1;"

		/* pass pointer to stack slot and r6 to subprog;
		 * r6 will be marked precise and spilled into fp-8 slot, which
		 * also should be marked precise
		 */
		"r1 = r10;"
		"r1 += -8;"
		"r2 = r6;"
		"call subprog_spill_reg_precise;"

		/* restore reg from stack; in this case we'll be carrying
		 * stack mask when going back into subprog through jump
		 * history
		 */
		"r7 = *(u64 *)(r10 - 8);"

		"r7 *= 4;"
		"r1 = %[vals];"
		/* here r7 is forced to be precise and has to be propagated
		 * back to the beginning, handling subprog call and logic
		 */
		"r1 += r7;"
		"r0 = *(u32 *)(r1 + 0);"
		"exit;"
		:
		: __imm_ptr(vals)
		: __clobber_common, "r6", "r7"
	);
}

__naked __noinline __used
static __u64 subprog_with_checkpoint(void)
{
	asm volatile (
		"r0 = 0;"
		/* guaranteed checkpoint if BPF_F_TEST_STATE_FREQ is used */
		"goto +0;"
		"exit;"
	);
}

char _license[] SEC("license") = "GPL";