linux-kernel - [PATCH AUTOSEL 5.17 062/149] libbpf: Fix accessing the first syscall argument on s390

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Date:   Fri,  1 Apr 2022 10:24:09 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Ilya Leoshkevich <iii@...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 5.17 062/149] libbpf: Fix accessing the first syscall argument on s390

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

[ Upstream commit 1f22a6f9f9a0f50218a11a0554709fd34a821fa3 ]

On s390, the first syscall argument should be accessed via orig_gpr2
(see arch/s390/include/asm/syscall.h). Currently gpr[2] is used
instead, leading to bpf_syscall_macro test failure.

orig_gpr2 cannot be added to 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: Andrii Nakryiko <andrii@...nel.org>
Signed-off-by: Ilya Leoshkevich <iii@...ux.ibm.com>
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
Link: https://lore.kernel.org/bpf/20220209021745.2215452-11-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 ad62c17919cf..92bf90e716ea 100644
--- a/tools/lib/bpf/bpf_tracing.h
+++ b/tools/lib/bpf/bpf_tracing.h
@@ -112,6 +112,10 @@
 
 #elif defined(bpf_target_s390)
 
+struct pt_regs___s390 {
+	unsigned long orig_gpr2;
+};
+
 /* s390 provides user_pt_regs instead of struct pt_regs to userspace */
 #define __PT_REGS_CAST(x) ((const user_pt_regs *)(x))
 #define __PT_PARM1_REG gprs[2]
@@ -124,6 +128,8 @@
 #define __PT_RC_REG gprs[2]
 #define __PT_SP_REG gprs[15]
 #define __PT_IP_REG psw.addr
+#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___s390 *)(x), orig_gpr2)
 
 #elif defined(bpf_target_arm)
 
-- 
2.34.1