[PATCH AUTOSEL 6.1 01/42] bpf: Check percpu map value size first

[PATCH AUTOSEL 6.1 01/42] bpf: Check percpu map value size first

[Sasha Levin]

From: Tao Chen <chen.dylane@gmail.com>

[ Upstream commit 1d244784be6b01162b732a5a7d637dfc024c3203 ]

Percpu map is often used, but the map value size limit often ignored,
like issue: https://github.com/iovisor/bcc/issues/2519. Actually,
percpu map value size is bound by PCPU_MIN_UNIT_SIZE, so we
can check the value size whether it exceeds PCPU_MIN_UNIT_SIZE first,
like percpu map of local_storage. Maybe the error message seems clearer
compared with "cannot allocate memory".

Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Tao Chen <chen.dylane@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240910144111.1464912-2-chen.dylane@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/bpf/arraymap.c | 3 +++
 kernel/bpf/hashtab.c  | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index c04e69f34e4d5..50b9bf57a4e3e 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -73,6 +73,9 @@ int array_map_alloc_check(union bpf_attr *attr)
 	/* avoid overflow on round_up(map->value_size) */
 	if (attr->value_size > INT_MAX)
 		return -E2BIG;
+	/* percpu map value size is bound by PCPU_MIN_UNIT_SIZE */
+	if (percpu && round_up(attr->value_size, 8) > PCPU_MIN_UNIT_SIZE)
+		return -E2BIG;
 
 	return 0;
 }
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 0c74cc9012d5c..dae9ed02a75be 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -455,6 +455,9 @@ static int htab_map_alloc_check(union bpf_attr *attr)
 		 * kmalloc-able later in htab_map_update_elem()
 		 */
 		return -E2BIG;
+	/* percpu map value size is bound by PCPU_MIN_UNIT_SIZE */
+	if (percpu && round_up(attr->value_size, 8) > PCPU_MIN_UNIT_SIZE)
+		return -E2BIG;
 
 	return 0;
 }
-- 
2.43.0

[PATCH AUTOSEL 6.1 05/42] bpf, x64: Fix a jit convergence issue

[Sasha Levin]

From: Yonghong Song <yonghong.song@linux.dev>

[ Upstream commit c8831bdbfbab672c006a18006d36932a494b2fd6 ]

Daniel Hodges reported a jit error when playing with a sched-ext program.
The error message is:
  unexpected jmp_cond padding: -4 bytes

But further investigation shows the error is actual due to failed
convergence. The following are some analysis:

  ...
  pass4, final_proglen=4391:
    ...
    20e:    48 85 ff                test   rdi,rdi
    211:    74 7d                   je     0x290
    213:    48 8b 77 00             mov    rsi,QWORD PTR [rdi+0x0]
    ...
    289:    48 85 ff                test   rdi,rdi
    28c:    74 17                   je     0x2a5
    28e:    e9 7f ff ff ff          jmp    0x212
    293:    bf 03 00 00 00          mov    edi,0x3

Note that insn at 0x211 is 2-byte cond jump insn for offset 0x7d (-125)
and insn at 0x28e is 5-byte jmp insn with offset -129.

  pass5, final_proglen=4392:
    ...
    20e:    48 85 ff                test   rdi,rdi
    211:    0f 84 80 00 00 00       je     0x297
    217:    48 8b 77 00             mov    rsi,QWORD PTR [rdi+0x0]
    ...
    28d:    48 85 ff                test   rdi,rdi
    290:    74 1a                   je     0x2ac
    292:    eb 84                   jmp    0x218
    294:    bf 03 00 00 00          mov    edi,0x3

Note that insn at 0x211 is 6-byte cond jump insn now since its offset
becomes 0x80 based on previous round (0x293 - 0x213 = 0x80). At the same
time, insn at 0x292 is a 2-byte insn since its offset is -124.

pass6 will repeat the same code as in pass4. pass7 will repeat the same
code as in pass5, and so on. This will prevent eventual convergence.

Passes 1-14 are with padding = 0. At pass15, padding is 1 and related
insn looks like:

    211:    0f 84 80 00 00 00       je     0x297
    217:    48 8b 77 00             mov    rsi,QWORD PTR [rdi+0x0]
    ...
    24d:    48 85 d2                test   rdx,rdx

The similar code in pass14:
    211:    74 7d                   je     0x290
    213:    48 8b 77 00             mov    rsi,QWORD PTR [rdi+0x0]
    ...
    249:    48 85 d2                test   rdx,rdx
    24c:    74 21                   je     0x26f
    24e:    48 01 f7                add    rdi,rsi
    ...

Before generating the following insn,
  250:    74 21                   je     0x273
"padding = 1" enables some checking to ensure nops is either 0 or 4
where
  #define INSN_SZ_DIFF (((addrs[i] - addrs[i - 1]) - (prog - temp)))
  nops = INSN_SZ_DIFF - 2

In this specific case,
  addrs[i] = 0x24e // from pass14
  addrs[i-1] = 0x24d // from pass15
  prog - temp = 3 // from 'test rdx,rdx' in pass15
so
  nops = -4
and this triggers the failure.

To fix the issue, we need to break cycles of je <-> jmp. For example,
in the above case, we have
  211:    74 7d                   je     0x290
the offset is 0x7d. If 2-byte je insn is generated only if
the offset is less than 0x7d (<= 0x7c), the cycle can be
break and we can achieve the convergence.

I did some study on other cases like je <-> je, jmp <-> je and
jmp <-> jmp which may cause cycles. Those cases are not from actual
reproducible cases since it is pretty hard to construct a test case
for them. the results show that the offset <= 0x7b (0x7b = 123) should
be enough to cover all cases. This patch added a new helper to generate 8-bit
cond/uncond jmp insns only if the offset range is [-128, 123].

Reported-by: Daniel Hodges <hodgesd@meta.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20240904221251.37109-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/net/bpf_jit_comp.c | 54 +++++++++++++++++++++++++++++++++++--
 1 file changed, 52 insertions(+), 2 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 7913440c0fd46..92db785a0a8eb 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -57,6 +57,56 @@ static bool is_imm8(int value)
 	return value <= 127 && value >= -128;
 }
 
+/*
+ * Let us limit the positive offset to be <= 123.
+ * This is to ensure eventual jit convergence For the following patterns:
+ * ...
+ * pass4, final_proglen=4391:
+ *   ...
+ *   20e:    48 85 ff                test   rdi,rdi
+ *   211:    74 7d                   je     0x290
+ *   213:    48 8b 77 00             mov    rsi,QWORD PTR [rdi+0x0]
+ *   ...
+ *   289:    48 85 ff                test   rdi,rdi
+ *   28c:    74 17                   je     0x2a5
+ *   28e:    e9 7f ff ff ff          jmp    0x212
+ *   293:    bf 03 00 00 00          mov    edi,0x3
+ * Note that insn at 0x211 is 2-byte cond jump insn for offset 0x7d (-125)
+ * and insn at 0x28e is 5-byte jmp insn with offset -129.
+ *
+ * pass5, final_proglen=4392:
+ *   ...
+ *   20e:    48 85 ff                test   rdi,rdi
+ *   211:    0f 84 80 00 00 00       je     0x297
+ *   217:    48 8b 77 00             mov    rsi,QWORD PTR [rdi+0x0]
+ *   ...
+ *   28d:    48 85 ff                test   rdi,rdi
+ *   290:    74 1a                   je     0x2ac
+ *   292:    eb 84                   jmp    0x218
+ *   294:    bf 03 00 00 00          mov    edi,0x3
+ * Note that insn at 0x211 is 6-byte cond jump insn now since its offset
+ * becomes 0x80 based on previous round (0x293 - 0x213 = 0x80).
+ * At the same time, insn at 0x292 is a 2-byte insn since its offset is
+ * -124.
+ *
+ * pass6 will repeat the same code as in pass4 and this will prevent
+ * eventual convergence.
+ *
+ * To fix this issue, we need to break je (2->6 bytes) <-> jmp (5->2 bytes)
+ * cycle in the above. In the above example je offset <= 0x7c should work.
+ *
+ * For other cases, je <-> je needs offset <= 0x7b to avoid no convergence
+ * issue. For jmp <-> je and jmp <-> jmp cases, jmp offset <= 0x7c should
+ * avoid no convergence issue.
+ *
+ * Overall, let us limit the positive offset for 8bit cond/uncond jmp insn
+ * to maximum 123 (0x7b). This way, the jit pass can eventually converge.
+ */
+static bool is_imm8_jmp_offset(int value)
+{
+	return value <= 123 && value >= -128;
+}
+
 static bool is_simm32(s64 value)
 {
 	return value == (s64)(s32)value;
@@ -1589,7 +1639,7 @@ st:			if (is_imm8(insn->off))
 				return -EFAULT;
 			}
 			jmp_offset = addrs[i + insn->off] - addrs[i];
-			if (is_imm8(jmp_offset)) {
+			if (is_imm8_jmp_offset(jmp_offset)) {
 				if (jmp_padding) {
 					/* To keep the jmp_offset valid, the extra bytes are
 					 * padded before the jump insn, so we subtract the
@@ -1671,7 +1721,7 @@ st:			if (is_imm8(insn->off))
 				break;
 			}
 emit_jmp:
-			if (is_imm8(jmp_offset)) {
+			if (is_imm8_jmp_offset(jmp_offset)) {
 				if (jmp_padding) {
 					/* To avoid breaking jmp_offset, the extra bytes
 					 * are padded before the actual jmp insn, so
-- 
2.43.0