77 lines
2.6 KiB
Diff
77 lines
2.6 KiB
Diff
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From d08dfdebb381427cbd8565994868926ba9bc4b40 Mon Sep 17 00:00:00 2001
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From: Eugene Syromyatnikov <evgsyr@gmail.com>
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Date: Wed, 30 Oct 2024 15:16:47 +0100
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Subject: [PATCH 188/190] linux/s390/get_scno.c: use NT_S390_SYSTEM_CALL if
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gprs[2] is clobbered
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The way the syscall number is retrieved currently relies on the kernel
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propagating it properly into gprs[2], which is not however always the case;
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apart of the situation where scno > NR_syscalls, there is also an issue
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of inspecting it during syscall restart (as it happens on attach, for
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example), when it is already clobbered by a ERESTART* errno. Luckily
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for strace, this issue has been already foreseen by the kernel
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developers, and support for retrieving syscall number on s390
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via a separate ptrace regset has been added by the Linux commit
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v3.2-rc1~109^2~34; 13 years later, it is time for it to fulfill
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its purpose and finally get utilised.
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* src/linux/s390/get_scno.c (arch_get_scno): Try to retrieve the syscall
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number by querying NT_S390_SYSTEM_CALL regset if gprs[2] contains an errno.
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Complements: v6.11-21-gc7e0ea6d712e "syscall: do not use uninitialized parts of struct ptrace_syscall_info"
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---
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src/linux/s390/get_scno.c | 34 ++++++++++++++++++++++++++++++++--
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1 file changed, 32 insertions(+), 2 deletions(-)
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diff --git a/src/linux/s390/get_scno.c b/src/linux/s390/get_scno.c
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index f0863e26d701..fdc94d025280 100644
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--- a/src/linux/s390/get_scno.c
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+++ b/src/linux/s390/get_scno.c
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@@ -9,11 +9,41 @@
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# define ARCH_REGSET s390_regset
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#endif
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+#ifndef NT_ARM_SYSTEM_CALL
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+# define NT_S390_SYSTEM_CALL 0x307
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+#endif
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+
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/* Return codes: 1 - ok, 0 - ignore, other - error. */
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static int
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arch_get_scno(struct tcb *tcp)
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{
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- tcp->scno = ARCH_REGSET.gprs[2] ?
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- ARCH_REGSET.gprs[2] : ARCH_REGSET.gprs[1];
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+ typeof(ARCH_REGSET.gprs[2]) gpr2 = ARCH_REGSET.gprs[2];
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+
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+ if (gpr2 > (typeof(gpr2)) (-4095ULL)) {
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+ /*
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+ * We are in restart_syscall and gprs[2] is clobbered
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+ * by the errno, using pulling the syscall number
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+ * via NT_S390_SYSTEM_CALL regset.
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+ */
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+ unsigned int scno;
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+ const struct iovec io = {
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+ .iov_base = &scno,
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+ .iov_len = sizeof(scno)
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+ };
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+ int rc = ptrace(PTRACE_GETREGSET, tcp->pid, NT_S390_SYSTEM_CALL,
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+ &io);
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+ if (rc && errno != ESRCH) {
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+ perror_func_msg("NT_S390_SYSTEM_CALL pid:%d", tcp->pid);
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+ return -1;
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+ }
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+ /*
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+ * The ptrace call returns thread.system_call, that stores raw
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+ * int_code, and the syscall number part is the lowest 16 bits
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+ * of it.
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+ */
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+ tcp->scno = scno & 0xffff;
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+ } else {
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+ tcp->scno = gpr2 ?: ARCH_REGSET.gprs[1];
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+ }
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return 1;
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}
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--
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2.28.0
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