lkml.org 
[lkml]   [2021]   [Aug]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 5.10 30/30] selftest/bpf: Verifier tests for var-off access
Date
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
tools/testing/selftests/bpf/verifier/var_off.c | 99 ++++++++++++++++++++++++-
1 file changed, 97 insertions(+), 2 deletions(-)

--- a/tools/testing/selftests/bpf/verifier/var_off.c
+++ b/tools/testing/selftests/bpf/verifier/var_off.c
@@ -31,15 +31,110 @@
* 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 = {
BPF_MOV64_IMM(BPF_REG_2, 6),

\
 
 \ /
  Last update: 2021-08-06 10:23    [W:0.126 / U:0.852 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site