Commit 6338a94d authored by Eduard Zingerman's avatar Eduard Zingerman Committed by Alexei Starovoitov
Browse files

selftests/bpf: Tests for uninitialized stack reads 



Three testcases to make sure that stack reads from uninitialized
locations are accepted by verifier when executed in privileged mode:
- read from a fixed offset;
- read from a variable offset;
- passing a pointer to stack to a helper converts
  STACK_INVALID to STACK_MISC.

Signed-off-by: default avatarEduard Zingerman <eddyz87@gmail.com>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230219200427.606541-3-eddyz87@gmail.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 6715df8d

tools/testing/selftests/bpf/prog_tests/uninit_stack.c

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// SPDX-License-Identifier: GPL-2.0



#include <test_progs.h>

#include "uninit_stack.skel.h"



void test_uninit_stack(void)

{

	RUN_TESTS(uninit_stack);

}

tools/testing/selftests/bpf/progs/uninit_stack.c

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// SPDX-License-Identifier: GPL-2.0



#include <linux/bpf.h>

#include <bpf/bpf_helpers.h>

#include "bpf_misc.h"



/* Read an uninitialized value from stack at a fixed offset */

SEC("socket")

__naked int read_uninit_stack_fixed_off(void *ctx)

{

	asm volatile ("					\

		r0 = 0;					\

		/* force stack depth to be 128 */	\

		*(u64*)(r10 - 128) = r1;		\

		r1 = *(u8 *)(r10 - 8 );			\

		r0 += r1;				\

		r1 = *(u8 *)(r10 - 11);			\

		r1 = *(u8 *)(r10 - 13);			\

		r1 = *(u8 *)(r10 - 15);			\

		r1 = *(u16*)(r10 - 16);			\

		r1 = *(u32*)(r10 - 32);			\

		r1 = *(u64*)(r10 - 64);			\

		/* read from a spill of a wrong size, it is a separate	\

		 * branch in check_stack_read_fixed_off()		\

		 */					\

		*(u32*)(r10 - 72) = r1;			\

		r1 = *(u64*)(r10 - 72);			\

		r0 = 0;					\

		exit;					\

"

		      ::: __clobber_all);

}



/* Read an uninitialized value from stack at a variable offset */

SEC("socket")

__naked int read_uninit_stack_var_off(void *ctx)

{

	asm volatile ("					\

		call %[bpf_get_prandom_u32];		\

		/* force stack depth to be 64 */	\

		*(u64*)(r10 - 64) = r0;			\

		r0 = -r0;				\

		/* give r0 a range [-31, -1] */		\

		if r0 s<= -32 goto exit_%=;		\

		if r0 s>= 0 goto exit_%=;		\

		/* access stack using r0 */		\

		r1 = r10;				\

		r1 += r0;				\

		r2 = *(u8*)(r1 + 0);			\

exit_%=:	r0 = 0;					\

		exit;					\

"

		      :

		      : __imm(bpf_get_prandom_u32)

		      : __clobber_all);

}



static __noinline void dummy(void) {}



/* Pass a pointer to uninitialized stack memory to a helper.

 * Passed memory block should be marked as STACK_MISC after helper call.

 */

SEC("socket")

__log_level(7) __msg("fp-104=mmmmmmmm")

__naked int helper_uninit_to_misc(void *ctx)

{

	asm volatile ("					\

		/* force stack depth to be 128 */	\

		*(u64*)(r10 - 128) = r1;		\

		r1 = r10;				\

		r1 += -128;				\

		r2 = 32;				\

		call %[bpf_trace_printk];		\

		/* Call to dummy() forces print_verifier_state(..., true),	\

		 * thus showing the stack state, matched by __msg().		\

		 */					\

		call %[dummy];				\

		r0 = 0;					\

		exit;					\

"

		      :

		      : __imm(bpf_trace_printk),

			__imm(dummy)

		      : __clobber_all);

}



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