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linux/tools/testing/selftests/bpf/progs/verifier_stack_ptr.c
Eduard Zingerman 022ac07508 bpf: use reg->var_off instead of reg->off for pointers 
This commit consolidates static and varying pointer offset tracking
logic. All offsets are now represented solely using `.var_off` and
min/max fields. The reasons are twofold:
- This simplifies pointer tracking code, as each relevant function
  needs to check the `.var_off` field anyway.
- It makes it easier to widen pointer registers for the purpose of loop
  convergence checks, by forgoing the `regsafe()` logic demanding
  `.off` fields to be identical.

The changes are spread across many functions and are hard to group
into smaller patches. Some of the logical changes include:
- Checks in __check_ptr_off_reg() are reordered so that the
  tnum_is_const() check is done before operating on reg->var_off.value.
- check_packet_access() now uses check_mem_region_access() to handle
  possible 'off' overflow cases.
- In check_helper_mem_access() utility functions like
  check_packet_access() are now called with 'off=0', as these utility
  functions now account for the complete register offset range.
- In check_reg_type() a call to __check_ptr_off_reg() is added before
  a call to btf_struct_ids_match(). This prevents
  btf_struct_ids_match() from potentially working on non-constant
  reg->var_off.value.
- regsafe() is relaxed to avoid comparing '.off' field for pointers.

As a precaution, the changes are verified in [1] by adding a pass
checking that no pointer has non-zero '.off' field on each
do_check_insn() iteration.

[1] https://github.com/eddyz87/bpf/tree/ptrs-off-migration

Notable selftests changes:
- `.var_off` value changed because it now combines static and varying
  offsets. Affected tests:
  - linked_list/incorrect_node_var_off
  - linked_list/incorrect_head_var_off2
  - verifier_align/packet_variable_offset

- Overflowing `smax_value` bound leads to a pointer with big negative
  or positive offset to be rejected immediately (previously overflowing
  `rX += const` instruction updated `.off` field avoiding the overflow).
  Affected tests:
  - verifier_align/dubious_pointer_arithmetic
  - verifier_bounds/var_off_insn_off_test1

- Invalid access to packet now reports full offset inside a packet.
  Affected tests:
  - verifier_direct_packet_access/test23_x_pkt_ptr_4

- A change in check_mem_region_access() behavior:
  when register `.smin_value` is negative, it reports
  "rX min value is negative..." before calling into __check_mem_access()
  which reports "invalid access to ...".
  In the tests below, the `.off` field was negative, while `.smin_value`
  remained positive. This is no longer the case after the changes in
  this commit. Affected tests:
  - verifier_gotox/jump_table_invalid_mem_acceess_neg
  - verifier_helper_packet_access/test15_cls_helper_fail_sub
  - verifier_helper_value_access/imm_out_of_bound_2
  - verifier_helper_value_access/reg_out_of_bound_2
  - verifier_meta_access/meta_access_test2
  - verifier_value_ptr_arith/known_scalar_from_different_maps
  - lower_oob_arith_test_1
  - value_ptr_known_scalar_3
  - access_value_ptr_known_scalar

- Usage of check_mem_region_access() instead of __check_mem_access()
  in check_packet_access() changes the reported message from
  "rX offset is outside ..." to "rX min/max value is outside ...".
  Affected tests:
  - verifier_xdp_direct_packet_access/*

- In check_func_arg_reg_off() the check for zero offset now operates
  on `.var_off` field instead of `.off` field. For tests where the
  pattern looks like `kfunc(reg_with_var_off, ...)`, this changes the
  reported error:
  - previously the error "variable ... access ... disallowed"
    was reported by __check_ptr_off_reg();
  - now "R1 must have zero offset ..." is reported by
    check_func_arg_reg_off() itself.
  Affected tests:
  - verifier/calls.c
    "calls: invalid kfunc call: PTR_TO_BTF_ID with variable offset"

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260212-ptrs-off-migration-v2-2-00820e4d3438@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2026-02-13 14:41:22 -08:00

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// SPDX-License-Identifier: GPL-2.0
/* Converted from tools/testing/selftests/bpf/verifier/stack_ptr.c */
#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include <limits.h>
#include "bpf_misc.h"
#define MAX_ENTRIES 11
struct test_val {
unsigned int index;
int foo[MAX_ENTRIES];
};
struct {
__uint(type, BPF_MAP_TYPE_ARRAY);
__uint(max_entries, 1);
__type(key, int);
__type(value, struct test_val);
} map_array_48b SEC(".maps");
SEC("socket")
__description("PTR_TO_STACK store/load")
__success __success_unpriv __retval(0xfaceb00c)
__naked void ptr_to_stack_store_load(void)
{
asm volatile (" \
r1 = r10; \
r1 += -10; \
r0 = 0xfaceb00c; \
*(u64*)(r1 + 2) = r0; \
r0 = *(u64*)(r1 + 2); \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK store/load - bad alignment on off")
__failure __msg("misaligned stack access off -8+2 size 8")
__failure_unpriv
__naked void load_bad_alignment_on_off(void)
{
asm volatile (" \
r1 = r10; \
r1 += -8; \
r0 = 0xfaceb00c; \
*(u64*)(r1 + 2) = r0; \
r0 = *(u64*)(r1 + 2); \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK store/load - bad alignment on reg")
__failure __msg("misaligned stack access off -10+8 size 8")
__failure_unpriv
__naked void load_bad_alignment_on_reg(void)
{
asm volatile (" \
r1 = r10; \
r1 += -10; \
r0 = 0xfaceb00c; \
*(u64*)(r1 + 8) = r0; \
r0 = *(u64*)(r1 + 8); \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK store/load - out of bounds low")
__failure __msg("invalid write to stack R1 off=-79992 size=8")
__msg_unpriv("R1 stack pointer arithmetic goes out of range")
__naked void load_out_of_bounds_low(void)
{
asm volatile (" \
r1 = r10; \
r1 += -80000; \
r0 = 0xfaceb00c; \
*(u64*)(r1 + 8) = r0; \
r0 = *(u64*)(r1 + 8); \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK store/load - out of bounds high")
__failure __msg("invalid write to stack R1 off=0 size=8")
__failure_unpriv
__naked void load_out_of_bounds_high(void)
{
asm volatile (" \
r1 = r10; \
r1 += -8; \
r0 = 0xfaceb00c; \
*(u64*)(r1 + 8) = r0; \
r0 = *(u64*)(r1 + 8); \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK check high 1")
__success __success_unpriv __retval(42)
__naked void to_stack_check_high_1(void)
{
asm volatile (" \
r1 = r10; \
r1 += -1; \
r0 = 42; \
*(u8*)(r1 + 0) = r0; \
r0 = *(u8*)(r1 + 0); \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK check high 2")
__success __success_unpriv __retval(42)
__naked void to_stack_check_high_2(void)
{
asm volatile (" \
r1 = r10; \
r0 = 42; \
*(u8*)(r1 - 1) = r0; \
r0 = *(u8*)(r1 - 1); \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK check high 3")
__success __failure_unpriv
__msg_unpriv("R1 stack pointer arithmetic goes out of range")
__retval(42)
__naked void to_stack_check_high_3(void)
{
asm volatile (" \
r1 = r10; \
r1 += 0; \
r0 = 42; \
*(u8*)(r1 - 1) = r0; \
r0 = *(u8*)(r1 - 1); \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK check high 4")
__failure __msg("invalid write to stack R1 off=0 size=1")
__msg_unpriv("R1 stack pointer arithmetic goes out of range")
__naked void to_stack_check_high_4(void)
{
asm volatile (" \
r1 = r10; \
r1 += 0; \
r0 = 42; \
*(u8*)(r1 + 0) = r0; \
r0 = *(u8*)(r1 + 0); \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK check high 5")
__failure __msg("invalid write to stack R1")
__msg_unpriv("R1 stack pointer arithmetic goes out of range")
__naked void to_stack_check_high_5(void)
{
asm volatile (" \
r1 = r10; \
r1 += %[__imm_0]; \
r0 = 42; \
*(u8*)(r1 + 0) = r0; \
r0 = *(u8*)(r1 + 0); \
exit; \
" :
: __imm_const(__imm_0, (1 << 29) - 1)
: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK check high 6")
__failure __msg("invalid write to stack")
__msg_unpriv("R1 stack pointer arithmetic goes out of range")
__naked void to_stack_check_high_6(void)
{
asm volatile (" \
r1 = r10; \
r1 += %[__imm_0]; \
r0 = 42; \
*(u8*)(r1 + %[shrt_max]) = r0; \
r0 = *(u8*)(r1 + %[shrt_max]); \
exit; \
" :
: __imm_const(__imm_0, (1 << 29) - 1),
__imm_const(shrt_max, SHRT_MAX)
: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK check high 7")
__failure __msg("fp pointer offset")
__msg_unpriv("R1 stack pointer arithmetic goes out of range")
__naked void to_stack_check_high_7(void)
{
asm volatile (" \
r1 = r10; \
r1 += %[__imm_0]; \
r1 += %[__imm_0]; \
r0 = 42; \
*(u8*)(r1 + %[shrt_max]) = r0; \
r0 = *(u8*)(r1 + %[shrt_max]); \
exit; \
" :
: __imm_const(__imm_0, (1 << 29) - 1),
__imm_const(shrt_max, SHRT_MAX)
: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK check low 1")
__success __success_unpriv __retval(42)
__naked void to_stack_check_low_1(void)
{
asm volatile (" \
r1 = r10; \
r1 += -512; \
r0 = 42; \
*(u8*)(r1 + 0) = r0; \
r0 = *(u8*)(r1 + 0); \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK check low 2")
__success __failure_unpriv
__msg_unpriv("R1 stack pointer arithmetic goes out of range")
__retval(42)
__naked void to_stack_check_low_2(void)
{
asm volatile (" \
r1 = r10; \
r1 += -513; \
r0 = 42; \
*(u8*)(r1 + 1) = r0; \
r0 = *(u8*)(r1 + 1); \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK check low 3")
__failure __msg("invalid write to stack R1 off=-513 size=1")
__msg_unpriv("R1 stack pointer arithmetic goes out of range")
__naked void to_stack_check_low_3(void)
{
asm volatile (" \
r1 = r10; \
r1 += -513; \
r0 = 42; \
*(u8*)(r1 + 0) = r0; \
r0 = *(u8*)(r1 + 0); \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK check low 4")
__failure __msg("math between fp pointer")
__failure_unpriv
__naked void to_stack_check_low_4(void)
{
asm volatile (" \
r1 = r10; \
r1 += %[int_min]; \
r0 = 42; \
*(u8*)(r1 + 0) = r0; \
r0 = *(u8*)(r1 + 0); \
exit; \
" :
: __imm_const(int_min, INT_MIN)
: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK check low 5")
__failure __msg("invalid write to stack")
__msg_unpriv("R1 stack pointer arithmetic goes out of range")
__naked void to_stack_check_low_5(void)
{
asm volatile (" \
r1 = r10; \
r1 += %[__imm_0]; \
r0 = 42; \
*(u8*)(r1 + 0) = r0; \
r0 = *(u8*)(r1 + 0); \
exit; \
" :
: __imm_const(__imm_0, -((1 << 29) - 1))
: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK check low 6")
__failure __msg("invalid write to stack")
__msg_unpriv("R1 stack pointer arithmetic goes out of range")
__naked void to_stack_check_low_6(void)
{
asm volatile (" \
r1 = r10; \
r1 += %[__imm_0]; \
r0 = 42; \
*(u8*)(r1 %[shrt_min]) = r0; \
r0 = *(u8*)(r1 %[shrt_min]); \
exit; \
" :
: __imm_const(__imm_0, -((1 << 29) - 1)),
__imm_const(shrt_min, SHRT_MIN)
: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK check low 7")
__failure __msg("fp pointer offset")
__msg_unpriv("R1 stack pointer arithmetic goes out of range")
__naked void to_stack_check_low_7(void)
{
asm volatile (" \
r1 = r10; \
r1 += %[__imm_0]; \
r1 += %[__imm_0]; \
r0 = 42; \
*(u8*)(r1 %[shrt_min]) = r0; \
r0 = *(u8*)(r1 %[shrt_min]); \
exit; \
" :
: __imm_const(__imm_0, -((1 << 29) - 1)),
__imm_const(shrt_min, SHRT_MIN)
: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK mixed reg/k, 1")
__success __success_unpriv __retval(42)
__naked void stack_mixed_reg_k_1(void)
{
asm volatile (" \
r1 = r10; \
r1 += -3; \
r2 = -3; \
r1 += r2; \
r0 = 42; \
*(u8*)(r1 + 0) = r0; \
r0 = *(u8*)(r1 + 0); \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK mixed reg/k, 2")
__success __success_unpriv __retval(42)
__naked void stack_mixed_reg_k_2(void)
{
asm volatile (" \
r0 = 0; \
*(u64*)(r10 - 8) = r0; \
r0 = 0; \
*(u64*)(r10 - 16) = r0; \
r1 = r10; \
r1 += -3; \
r2 = -3; \
r1 += r2; \
r0 = 42; \
*(u8*)(r1 + 0) = r0; \
r5 = r10; \
r0 = *(u8*)(r5 - 6); \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK mixed reg/k, 3")
__success __success_unpriv __retval(-3)
__naked void stack_mixed_reg_k_3(void)
{
asm volatile (" \
r1 = r10; \
r1 += -3; \
r2 = -3; \
r1 += r2; \
r0 = 42; \
*(u8*)(r1 + 0) = r0; \
r0 = r2; \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK reg")
__success __success_unpriv __retval(42)
__naked void ptr_to_stack_reg(void)
{
asm volatile (" \
r1 = r10; \
r2 = -3; \
r1 += r2; \
r0 = 42; \
*(u8*)(r1 + 0) = r0; \
r0 = *(u8*)(r1 + 0); \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("stack pointer arithmetic")
__success __success_unpriv __retval(0)
__naked void stack_pointer_arithmetic(void)
{
asm volatile (" \
r1 = 4; \
goto l0_%=; \
l0_%=: r7 = r10; \
r7 += -10; \
r7 += -10; \
r2 = r7; \
r2 += r1; \
r0 = 0; \
*(u32*)(r2 + 4) = r0; \
r2 = r7; \
r2 += 8; \
r0 = 0; \
*(u32*)(r2 + 4) = r0; \
r0 = 0; \
exit; \
" ::: __clobber_all);
}
SEC("tc")
__description("store PTR_TO_STACK in R10 to array map using BPF_B")
__success __retval(42)
__naked void array_map_using_bpf_b(void)
{
asm volatile (" \
/* Load pointer to map. */ \
r2 = r10; \
r2 += -8; \
r1 = 0; \
*(u64*)(r2 + 0) = r1; \
r1 = %[map_array_48b] ll; \
call %[bpf_map_lookup_elem]; \
if r0 != 0 goto l0_%=; \
r0 = 2; \
exit; \
l0_%=: r1 = r0; \
/* Copy R10 to R9. */ \
r9 = r10; \
/* Pollute other registers with unaligned values. */\
r2 = -1; \
r3 = -1; \
r4 = -1; \
r5 = -1; \
r6 = -1; \
r7 = -1; \
r8 = -1; \
/* Store both R9 and R10 with BPF_B and read back. */\
*(u8*)(r1 + 0) = r10; \
r2 = *(u8*)(r1 + 0); \
*(u8*)(r1 + 0) = r9; \
r3 = *(u8*)(r1 + 0); \
/* Should read back as same value. */ \
if r2 == r3 goto l1_%=; \
r0 = 1; \
exit; \
l1_%=: r0 = 42; \
exit; \
" :
: __imm(bpf_map_lookup_elem),
__imm_addr(map_array_48b)
: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK stack size > 512")
__failure __msg("invalid write to stack R1 off=-520 size=8")
__naked void stack_check_size_gt_512(void)
{
asm volatile (" \
r1 = r10; \
r1 += -520; \
r0 = 42; \
*(u64*)(r1 + 0) = r0; \
exit; \
" ::: __clobber_all);
}
#ifdef __BPF_FEATURE_MAY_GOTO
SEC("socket")
__description("PTR_TO_STACK stack size 512 with may_goto with jit")
__load_if_JITed()
__success __retval(42)
__naked void stack_check_size_512_with_may_goto_jit(void)
{
asm volatile (" \
r1 = r10; \
r1 += -512; \
r0 = 42; \
*(u32*)(r1 + 0) = r0; \
may_goto l0_%=; \
r2 = 100; \
l0_%=: \
exit; \
" ::: __clobber_all);
}
SEC("socket")
__description("PTR_TO_STACK stack size 512 with may_goto without jit")
__load_if_no_JITed()
__failure __msg("stack size 520(extra 8) is too large")
__naked void stack_check_size_512_with_may_goto(void)
{
asm volatile (" \
r1 = r10; \
r1 += -512; \
r0 = 42; \
*(u32*)(r1 + 0) = r0; \
may_goto l0_%=; \
r2 = 100; \
l0_%=: \
exit; \
" ::: __clobber_all);
}
#endif
char _license[] SEC("license") = "GPL";
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