Merge branch 'bpf-fix-call-offset-truncation-and-oob-read-in-bpf_patch_call_args'

Merge branch 'bpf-fix-call-offset-truncation-and-oob-read-in-bpf_patch_call_args'

Yazhou Tang says:

====================
bpf: Fix call offset truncation and OOB read in bpf_patch_call_args()

From: Yazhou Tang <tangyazhou518@outlook.com>

This patchset addresses a silent truncation bug in the BPF verifier that
occurs when a bpf-to-bpf call involves a massive relative jump offset.
Additionally, it fixes a pre-existing out-of-bounds (OOB) read issue
in the interpreter fallback path.

Because the BPF instruction set utilizes a 32-bit imm field for bpf-to-bpf
calls, implicitly downcasting it to the 16-bit insn->off in bpf_patch_call_args()
causes incorrect call targets or subprog ID resolution for large BPF programs.
While fixing this by swapping the imm and off fields, it was discovered that
the original code also had a load-time OOB read vulnerability when the stack
depth exceeds MAX_BPF_STACK during JIT fallback.

Patch 1/3 fixes the pre-existing OOB read in bpf_patch_call_args(). It
changes the function to return an int and explicitly rejects the JIT
fallback if the stack depth exceeds MAX_BPF_STACK, preventing a potential
stack buffer overflow.

Patch 2/3 fixes the s16 truncation bug.
1. Keep the original imm field unchanged and use the off field to store
   the interpreter function index.
2. Adjust the JMP_CALL_ARGS case in ___bpf_prog_run() accordingly.
3. Restore the legacy xlated dump layout in bpf_insn_prepare_dump().

Patch 3/3 introduces a selftest for this fix.
---

Change log:

v10:
1. Make the error log in patch 1/3 more clear. (Kuohai)
2. Drop bpftool and disasm_helpers.c changes, and instead restore the
   legacy xlated dump layout in bpf_insn_prepare_dump(). This avoids
   requiring bpftool compatibility handling. (Quentin and Alexei)

v9: https://lore.kernel.org/bpf/20260429171904.107244-1-tangyazhou@zju.edu.cn/
1. Modify the selftest in patch 3/3: use __clobber_all in inline asm.
   (Sashiko AI reviewer)

v8: https://lore.kernel.org/bpf/20260429105608.92741-1-tangyazhou@zju.edu.cn/
1. Update cfg_partition_funcs() in bpftool to use insn->imm for call target
   calculation. (Sashiko AI reviewer)
2. Modify the selftest in patch 3/3: add a large padding before the call
   instruction, preventing the kernel panic on kernel without the fix.
   (Sashiko AI reviewer)
3. Modify the selftest in patch 3/3: make it more clear.

v7: https://lore.kernel.org/bpf/20260421144504.823756-1-tangyazhou@zju.edu.cn/
1. Rebase the patchset to the bpf-next tree to resolve the apply conflict.
   (Alexei)
2. Add Patch 1/3 to properly fix a pre-existing OOB read in bpf_patch_call_args().
   (Sashiko AI reviewer)

v6: https://lore.kernel.org/bpf/20260412170334.716778-1-tangyazhou@zju.edu.cn/
1. Use a different but clearer approach to resolve this issue: keeping
   the original imm field unchanged and using the off field to store the
   interpreter function index. (Kuohai)
2. Update the related dumper code and remove a previous workaround in the
   selftests disasm helpers, which is no longer needed after this fix.

v5: https://lore.kernel.org/bpf/20260326090133.221957-1-tangyazhou@zju.edu.cn/
1. Some minor changes in commit messages. (AI Reviewer)

v4: https://lore.kernel.org/bpf/20260326063329.10031-1-tangyazhou@zju.edu.cn/
1. Remove some redundant commit messages of patch 2/3. (Emil)
2. Change the number of instructions in padding_subprog() from 200,000
   to 32,765, which is the minimum number of instructions required to
   trigger the verifier failure. (Emil)

v3: https://lore.kernel.org/bpf/20260323122254.98540-1-tangyazhou@zju.edu.cn/
1. Resend to fix a typo in v2 and add "Fixes" tag. The rest of the changes
   are identical to v2.

v2 (incorrect): https://lore.kernel.org/bpf/20260323081748.106603-1-tangyazhou@zju.edu.cn/
1. Move the s16 boundary check from fixup_call_args() to bpf_patch_call_args(),
   and change the return type of bpf_patch_call_args() to int. (Emil)
2. Add Patch 3/3 to fix the incorrect subprog ID in dumped bpf_pseudo_call
   instructions, which is caused by the same truncation issue. (Puranjay)
3. Refine the new selftest for clarity and add detailed comments explaining
   the test design. (Emil)

v1: https://lore.kernel.org/bpf/20260316190220.113417-1-tangyazhou@zju.edu.cn/
====================

Link: https://patch.msgid.link/20260506094714.419842-1-tangyazhou@zju.edu.cn
Signed-off-by: Alexei Starovoitov <ast@kernel.org>