uninit_stack.c

 1// SPDX-License-Identifier: GPL-2.0
 2
 3#include <linux/bpf.h>
 4#include <bpf/bpf_helpers.h>
 5#include "bpf_misc.h"
 6
 7/* Read an uninitialized value from stack at a fixed offset */
 8SEC("socket")
 9__naked int read_uninit_stack_fixed_off(void *ctx)
10{
11	asm volatile ("					\
12		r0 = 0;					\
13		/* force stack depth to be 128 */	\
14		*(u64*)(r10 - 128) = r1;		\
15		r1 = *(u8 *)(r10 - 8 );			\
16		r0 += r1;				\
17		r1 = *(u8 *)(r10 - 11);			\
18		r1 = *(u8 *)(r10 - 13);			\
19		r1 = *(u8 *)(r10 - 15);			\
20		r1 = *(u16*)(r10 - 16);			\
21		r1 = *(u32*)(r10 - 32);			\
22		r1 = *(u64*)(r10 - 64);			\
23		/* read from a spill of a wrong size, it is a separate	\
24		 * branch in check_stack_read_fixed_off()		\
25		 */					\
26		*(u32*)(r10 - 72) = r1;			\
27		r1 = *(u64*)(r10 - 72);			\
28		r0 = 0;					\
29		exit;					\
30"
31		      ::: __clobber_all);
32}
33
34/* Read an uninitialized value from stack at a variable offset */
35SEC("socket")
36__naked int read_uninit_stack_var_off(void *ctx)
37{
38	asm volatile ("					\
39		call %[bpf_get_prandom_u32];		\
40		/* force stack depth to be 64 */	\
41		*(u64*)(r10 - 64) = r0;			\
42		r0 = -r0;				\
43		/* give r0 a range [-31, -1] */		\
44		if r0 s<= -32 goto exit_%=;		\
45		if r0 s>= 0 goto exit_%=;		\
46		/* access stack using r0 */		\
47		r1 = r10;				\
48		r1 += r0;				\
49		r2 = *(u8*)(r1 + 0);			\
50exit_%=:	r0 = 0;					\
51		exit;					\
52"
53		      :
54		      : __imm(bpf_get_prandom_u32)
55		      : __clobber_all);
56}
57
58static __noinline void dummy(void) {}
59
60/* Pass a pointer to uninitialized stack memory to a helper.
61 * Passed memory block should be marked as STACK_MISC after helper call.
62 */
63SEC("socket")
64__log_level(7) __msg("fp-104=mmmmmmmm")
65__naked int helper_uninit_to_misc(void *ctx)
66{
67	asm volatile ("					\
68		/* force stack depth to be 128 */	\
69		*(u64*)(r10 - 128) = r1;		\
70		r1 = r10;				\
71		r1 += -128;				\
72		r2 = 32;				\
73		r3 = 0;					\
74		call %[bpf_probe_read_user];		\
75		/* Call to dummy() forces print_verifier_state(..., true),	\
76		 * thus showing the stack state, matched by __msg().		\
77		 */					\
78		call %[dummy];				\
79		r0 = 0;					\
80		exit;					\
81"
82		      :
83		      : __imm(bpf_probe_read_user),
84			__imm(dummy)
85		      : __clobber_all);
86}
87
88char _license[] SEC("license") = "GPL";