From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4F2651553AA; Wed, 4 Jun 2025 00:52:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748998344; cv=none; b=V6fYG1OTWFI7UlGC5/BFEWI+eG/ehR5eV/BtLlP5V/dgwGORtWqwBHW8d1edTfvbRYJkXm8yeCJUNGIfziDiosiHt3F1xyF4Gtj7wpwbN70SVUwOBu9zP5dA55xOQWLgAVli/CGl27FGwnXhhxvZ4SAz4bsZCXaNkrM5ANz4jpA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748998344; c=relaxed/simple; bh=vSKf8W4u98bfM3nM7OyYIlMKPETQuvo5HAQPKg4FMyM=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=dIPSUJ+Oq8wAdH1Wi9EabO6MqD9lciEGS6QjpMge6/N/zwuIc3TMNk50aDBkLihSw5jOeh7PesvNWnSU0Qg6hIbL/tObC/PYuiIq5l29WXEG7Vow7oYjXBiEy7WH34hj9GxDOOfWT1qZbpKU9AEbr6RaTh8b/A8dpTSKcxvmj/I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PZ8lKvQG; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="PZ8lKvQG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EE61BC4CEF1; Wed, 4 Jun 2025 00:52:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1748998344; bh=vSKf8W4u98bfM3nM7OyYIlMKPETQuvo5HAQPKg4FMyM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=PZ8lKvQG/W6TVrQWAVslIpmqEMK59CK8OsYQo8DgoHLk1MK9ptdFH4pxOJnPkB1pR Z4YvMcq00ITA2T62mIx+buDvdzdYgvZl64Hx/EiU9U92UnEJtaxJgypj0XfG8HBoNx 5jVf84KbXz6dmPdjIIM5dHPbGZOAxvkaOUADc2licHcEanWZk1UVrWb67VSDAUhDpS kIcfdrWD/pmF5Cp+ORD8mFncidR9p9yVClEPDRchgMOLD6Oh+rd4Kx+Raxg8cUmm0m 25oS1JljVvgnhZbRAb78ymOljNeeAnpOhUMYs6KXVgAN9wM8xDtgBPKent2qMUl2Pw +4DA4uVKqh2RA== From: Sasha Levin To: patches@lists.linux.dev, stable@vger.kernel.org Cc: Ilya Leoshkevich , Martin KaFai Lau , Alexei Starovoitov , Sasha Levin , martin.lau@linux.dev, daniel@iogearbox.net, andrii@kernel.org, bpf@vger.kernel.org, netdev@vger.kernel.org Subject: [PATCH AUTOSEL 6.15 048/118] bpf: Pass the same orig_call value to trampoline functions Date: Tue, 3 Jun 2025 20:49:39 -0400 Message-Id: <20250604005049.4147522-48-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250604005049.4147522-1-sashal@kernel.org> References: <20250604005049.4147522-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.15 Content-Transfer-Encoding: 8bit From: Ilya Leoshkevich [ Upstream commit 94bde253d3ae5d8a01cb958663b12daef1d06574 ] There is currently some confusion in the s390x JIT regarding whether orig_call can be NULL and what that means. Originally the NULL value was used to distinguish the struct_ops case, but this was superseded by BPF_TRAMP_F_INDIRECT (see commit 0c970ed2f87c ("s390/bpf: Fix indirect trampoline generation"). The remaining reason to have this check is that NULL can actually be passed to the arch_bpf_trampoline_size() call - but not to the respective arch_prepare_bpf_trampoline()! call - by bpf_struct_ops_prepare_trampoline(). Remove this asymmetry by passing stub_func to both functions, so that JITs may rely on orig_call never being NULL. Signed-off-by: Ilya Leoshkevich Acked-by: Martin KaFai Lau Link: https://lore.kernel.org/r/20250512221911.61314-2-iii@linux.ibm.com Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- **YES** This commit should be backported to stable kernel trees. ## Analysis **Nature of the Fix:** This commit addresses an asymmetry in the BPF trampoline infrastructure where `NULL` could be passed to `arch_bpf_trampoline_size()` but not to `arch_prepare_bpf_trampoline()`. The fix ensures that `stub_func` is consistently passed to both functions, allowing JIT implementations to rely on `orig_call` never being `NULL`. **Code Changes Analysis:** The change is minimal and surgical - only one line in `kernel/bpf/bpf_struct_ops.c`: ```c - size = arch_bpf_trampoline_size(model, flags, tlinks, NULL); + size = arch_bpf_trampoline_size(model, flags, tlinks, stub_func); ``` This passes `stub_func` instead of `NULL` to `arch_bpf_trampoline_size()`, creating consistency with the `arch_prepare_bpf_trampoline()` call on line 620 which already receives `stub_func`. **Why This Should Be Backported:** 1. **Fixes Architectural Inconsistency:** Based on the repository analysis, this addresses confusion in JIT implementations (particularly s390x) about when `orig_call` can be `NULL` and what that signifies. 2. **Prevents Potential Crashes:** The repository history shows that similar asymmetries in BPF trampoline handling caused crashes on architectures like RISC-V and incorrect code generation on s390x. 3. **Minimal Risk:** The change is extremely contained - it only affects the parameter passed to `arch_bpf_trampoline_size()` in the struct_ops path. Since this function is used for size calculation, passing a valid function pointer instead of `NULL` should not break existing functionality. 4. **Follows Stable Tree Criteria:** - **Important bugfix:** Prevents JIT confusion and potential incorrect behavior - **Minimal risk:** Single line change with clear semantics - **Confined to subsystem:** Only affects BPF struct_ops trampoline generation - **No architectural changes:** Does not modify core BPF infrastructure 5. **Related Historical Precedent:** Looking at the similar commits in the analysis, commit #3 (s390/bpf: Let arch_prepare_bpf_trampoline return program size) was marked "YES" for backporting, and it was a similar cleanup/consistency fix for the BPF trampoline infrastructure. 6. **Prevents Future Issues:** This fix eliminates a source of confusion for JIT maintainers and ensures all architectures can implement consistent `NULL` checking logic. The fix aligns with the principle established in commit 0c970ed2f87c that JITs should use the `BPF_TRAMP_F_INDIRECT` flag rather than checking for `NULL` parameters, and this change supports that by ensuring parameters are never `NULL` in the first place. kernel/bpf/bpf_struct_ops.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c index db13ee70d94d5..96113633e391a 100644 --- a/kernel/bpf/bpf_struct_ops.c +++ b/kernel/bpf/bpf_struct_ops.c @@ -601,7 +601,7 @@ int bpf_struct_ops_prepare_trampoline(struct bpf_tramp_links *tlinks, if (model->ret_size > 0) flags |= BPF_TRAMP_F_RET_FENTRY_RET; - size = arch_bpf_trampoline_size(model, flags, tlinks, NULL); + size = arch_bpf_trampoline_size(model, flags, tlinks, stub_func); if (size <= 0) return size ? : -EFAULT; -- 2.39.5