From: Andrei Matei andreimatei1@gmail.com
commit 7a22930c4179b51352f2ec9feb35167cbe79afd9 upstream
Add tests for the new functionality - reading and writing to the stack through a variable-offset pointer.
Signed-off-by: Andrei Matei andreimatei1@gmail.com Signed-off-by: Alexei Starovoitov ast@kernel.org Link: https://lore.kernel.org/bpf/20210207011027.676572-4-andreimatei1@gmail.com Signed-off-by: Ovidiu Panait ovidiu.panait@windriver.com --- .../testing/selftests/bpf/verifier/var_off.c | 99 ++++++++++++++++++- 1 file changed, 97 insertions(+), 2 deletions(-)
diff --git a/tools/testing/selftests/bpf/verifier/var_off.c b/tools/testing/selftests/bpf/verifier/var_off.c index 49b78a1a261b..eab1f7f56e2f 100644 --- a/tools/testing/selftests/bpf/verifier/var_off.c +++ b/tools/testing/selftests/bpf/verifier/var_off.c @@ -31,14 +31,109 @@ * we don't know which */ BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_10), - /* dereference it */ + /* dereference it for a stack read */ + BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_2, 0), + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + }, + .result = ACCEPT, + .result_unpriv = REJECT, + .errstr_unpriv = "R2 variable stack access prohibited for !root", + .prog_type = BPF_PROG_TYPE_CGROUP_SKB, +}, +{ + "variable-offset stack read, uninitialized", + .insns = { + /* Get an unknown value */ + BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, 0), + /* Make it small and 4-byte aligned */ + BPF_ALU64_IMM(BPF_AND, BPF_REG_2, 4), + BPF_ALU64_IMM(BPF_SUB, BPF_REG_2, 8), + /* add it to fp. We now have either fp-4 or fp-8, but + * we don't know which + */ + BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_10), + /* dereference it for a stack read */ BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_2, 0), + BPF_MOV64_IMM(BPF_REG_0, 0), BPF_EXIT_INSN(), }, - .errstr = "variable stack access var_off=(0xfffffffffffffff8; 0x4)", .result = REJECT, + .errstr = "invalid variable-offset read from stack R2", .prog_type = BPF_PROG_TYPE_LWT_IN, }, +{ + "variable-offset stack write, priv vs unpriv", + .insns = { + /* Get an unknown value */ + BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, 0), + /* Make it small and 8-byte aligned */ + BPF_ALU64_IMM(BPF_AND, BPF_REG_2, 8), + BPF_ALU64_IMM(BPF_SUB, BPF_REG_2, 16), + /* Add it to fp. We now have either fp-8 or fp-16, but + * we don't know which + */ + BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_10), + /* Dereference it for a stack write */ + BPF_ST_MEM(BPF_DW, BPF_REG_2, 0, 0), + /* Now read from the address we just wrote. This shows + * that, after a variable-offset write, a priviledged + * program can read the slots that were in the range of + * that write (even if the verifier doesn't actually know + * if the slot being read was really written to or not. + */ + BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_2, 0), + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + }, + /* Variable stack access is rejected for unprivileged. + */ + .errstr_unpriv = "R2 variable stack access prohibited for !root", + .result_unpriv = REJECT, + .result = ACCEPT, +}, +{ + "variable-offset stack write clobbers spilled regs", + .insns = { + /* Dummy instruction; needed because we need to patch the next one + * and we can't patch the first instruction. + */ + BPF_MOV64_IMM(BPF_REG_6, 0), + /* Make R0 a map ptr */ + BPF_LD_MAP_FD(BPF_REG_0, 0), + /* Get an unknown value */ + BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, 0), + /* Make it small and 8-byte aligned */ + BPF_ALU64_IMM(BPF_AND, BPF_REG_2, 8), + BPF_ALU64_IMM(BPF_SUB, BPF_REG_2, 16), + /* Add it to fp. We now have either fp-8 or fp-16, but + * we don't know which. + */ + BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_10), + /* Spill R0(map ptr) into stack */ + BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_0, -8), + /* Dereference the unknown value for a stack write */ + BPF_ST_MEM(BPF_DW, BPF_REG_2, 0, 0), + /* Fill the register back into R2 */ + BPF_LDX_MEM(BPF_DW, BPF_REG_2, BPF_REG_10, -8), + /* Try to dereference R2 for a memory load */ + BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_2, 8), + BPF_EXIT_INSN(), + }, + .fixup_map_hash_8b = { 1 }, + /* The unpriviledged case is not too interesting; variable + * stack access is rejected. + */ + .errstr_unpriv = "R2 variable stack access prohibited for !root", + .result_unpriv = REJECT, + /* In the priviledged case, dereferencing a spilled-and-then-filled + * register is rejected because the previous variable offset stack + * write might have overwritten the spilled pointer (i.e. we lose track + * of the spilled register when we analyze the write). + */ + .errstr = "R2 invalid mem access 'inv'", + .result = REJECT, +}, { "indirect variable-offset stack access, unbounded", .insns = {