selftests/bpf: Test packet range of pointers sharing an idgrafted

Add tests where two packet pointers share an id and tightening one
pointer's umax from its var_off would put it less than their constant
distance from the other's umax: with an index & 0x38 capped at 50, the
base pointer keeps umax 50, so the pointer 8 bytes further on must keep
umax 58, even though its known bits allow at most 56.

These refused a valid program or accepted an out-of-bounds access before
the fix:

- check the advanced copy, load through the base: valid, was refused;
- check the base, load the byte at base + 1 through a copy advanced by
  8: was accepted;
- check base + 4, load 4 bytes at base + 2 through base + 8: reads two
  bytes past the checked range, was accepted;
- the same as the second with data_meta pointers checked against data:
  was accepted.

These pass with and without the fix and cover nearby paths:

- subtract an unknown scalar from a checked pointer and load below it
  (the range is kept across a new id);
- reach a load through two paths whose checks cover 8 and 7 bytes after
  the loaded pointer; the second path must not be pruned by the first;
- spill a copy of a pointer, check the pointer, fill the copy and load
  one byte past the checked range: the load is refused, and the copy
  has the range of the check.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20261001145255.855630-2-alexei.starovoitov@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/arch/powerpc/lib/string.S b/arch/powerpc/lib/string.S
new file mode 100644
index 000000000..c3f5e7d31
--- /dev/null
+++ b/arch/powerpc/lib/string.S
@@ -0,0 +1,43 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * String handling functions for PowerPC.
+ *
+ * Copyright (C) 1996 Paul Mackerras.
+ */
+#include <linux/export.h>
+#include <asm/ppc_asm.h>
+#include <asm/cache.h>
+
+	.text
+	
+_GLOBAL(strncmp)
+	PPC_LCMPI 0,r5,0
+	beq-	2f
+	mtctr	r5
+	addi	r5,r3,-1
+	addi	r4,r4,-1
+	.balign IFETCH_ALIGN_BYTES
+1:	lbzu	r3,1(r5)
+	cmpwi	1,r3,0
+	lbzu	r0,1(r4)
+	subf.	r3,r0,r3
+	beqlr	1
+	bdnzt	eq,1b
+	blr
+2:	li	r3,0
+	blr
+EXPORT_SYMBOL(strncmp)
+
+_GLOBAL(memchr)
+	PPC_LCMPI 0,r5,0
+	beq-	2f
+	mtctr	r5
+	addi	r3,r3,-1
+	.balign IFETCH_ALIGN_BYTES
+1:	lbzu	r0,1(r3)
+	cmpw	0,r0,r4
+	bdnzf	2,1b
+	beqlr
+2:	li	r3,0
+	blr
+EXPORT_SYMBOL(memchr)