linux-kernel - [PATCH AUTOSEL 5.17 061/149] libbpf: Fix accessing the first syscall argument on arm64

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Date:   Fri,  1 Apr 2022 10:24:08 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Ilya Leoshkevich <iii@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Sasha Levin <sashal@...nel.org>, ast@...nel.org,
        daniel@...earbox.net, netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH AUTOSEL 5.17 061/149] libbpf: Fix accessing the first syscall argument on arm64

From: Ilya Leoshkevich <iii@...ux.ibm.com>

[ Upstream commit fbca4a2f649730b67488a8b36140ce4d2cf13c63 ]

On arm64, the first syscall argument should be accessed via orig_x0
(see arch/arm64/include/asm/syscall.h). Currently regs[0] is used
instead, leading to bpf_syscall_macro test failure.

orig_x0 cannot be added to struct user_pt_regs, since its layout is a
part of the ABI. Therefore provide access to it only through
PT_REGS_PARM1_CORE_SYSCALL() by using a struct pt_regs flavor.

Reported-by: Heiko Carstens <hca@...ux.ibm.com>
Signed-off-by: Ilya Leoshkevich <iii@...ux.ibm.com>
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
Link: https://lore.kernel.org/bpf/20220209021745.2215452-10-iii@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 tools/lib/bpf/bpf_tracing.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/lib/bpf/bpf_tracing.h b/tools/lib/bpf/bpf_tracing.h
index d40b87c0e4b9..ad62c17919cf 100644
--- a/tools/lib/bpf/bpf_tracing.h
+++ b/tools/lib/bpf/bpf_tracing.h
@@ -140,6 +140,10 @@
 
 #elif defined(bpf_target_arm64)
 
+struct pt_regs___arm64 {
+	unsigned long orig_x0;
+};
+
 /* arm64 provides struct user_pt_regs instead of struct pt_regs to userspace */
 #define __PT_REGS_CAST(x) ((const struct user_pt_regs *)(x))
 #define __PT_PARM1_REG regs[0]
@@ -152,6 +156,8 @@
 #define __PT_RC_REG regs[0]
 #define __PT_SP_REG sp
 #define __PT_IP_REG pc
+#define PT_REGS_PARM1_SYSCALL(x) ({ _Pragma("GCC error \"use PT_REGS_PARM1_CORE_SYSCALL() instead\""); 0l; })
+#define PT_REGS_PARM1_CORE_SYSCALL(x) BPF_CORE_READ((const struct pt_regs___arm64 *)(x), orig_x0)
 
 #elif defined(bpf_target_mips)
 
-- 
2.34.1