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From: Ali Raza <aliraza@bu.edu>
To: linux-kernel@vger.kernel.org
Cc: corbet@lwn.net, masahiroy@kernel.org, michal.lkml@markovi.net,
	ndesaulniers@google.com, tglx@linutronix.de, mingo@redhat.com,
	bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com,
	luto@kernel.org, ebiederm@xmission.com, keescook@chromium.org,
	peterz@infradead.org, viro@zeniv.linux.org.uk, arnd@arndb.de,
	juri.lelli@redhat.com, vincent.guittot@linaro.org,
	dietmar.eggemann@arm.com, rostedt@goodmis.org,
	bsegall@google.com, mgorman@suse.de, bristot@redhat.com,
	vschneid@redhat.com, pbonzini@redhat.com, jpoimboe@kernel.org,
	linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	linux-arch@vger.kernel.org, x86@kernel.org, rjones@redhat.com,
	munsoner@bu.edu, tommyu@bu.edu, drepper@redhat.com,
	lwoodman@redhat.com, mboydmcse@gmail.com, okrieg@bu.edu,
	rmancuso@bu.edu, Ali Raza <aliraza@bu.edu>
Subject: [RFC UKL 07/10] x86/signal: Adjust signal handler register values and return frame
Date: Mon,  3 Oct 2022 18:21:30 -0400	[thread overview]
Message-ID: <20221003222133.20948-8-aliraza@bu.edu> (raw)
In-Reply-To: <20221003222133.20948-1-aliraza@bu.edu>

For a UKL thread, returning to a signal handler is not done with iret or
sysret.  This means we need to adjust the way the return stack frame is
handled for these threads.  When constructing the signal frame, we leave
the previous frame in place because we will return to it from the signal
handler.  We also leave space for pushing eflags and the return address.
UKL threads will only use the __KERNEL_DS value in the ss register and 0xC3
in the cs register.

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Michal Marek <michal.lkml@markovi.net>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>

Co-developed-by: Eric B Munson <munsoner@bu.edu>
Signed-off-by: Eric B Munson <munsoner@bu.edu>
Co-developed-by: Ali Raza <aliraza@bu.edu>
Signed-off-by: Ali Raza <aliraza@bu.edu>
---
 arch/x86/kernel/signal.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 9c7265b524c7..a95c12f6dac6 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -121,8 +121,10 @@ static bool restore_sigcontext(struct pt_regs *regs,
 #endif /* CONFIG_X86_64 */
 
 	/* Get CS/SS and force CPL3 */
-	regs->cs = sc.cs | 0x03;
-	regs->ss = sc.ss | 0x03;
+	if (!is_ukl_thread()) {
+		regs->cs = sc.cs | 0x03;
+		regs->ss = sc.ss | 0x03;
+	}
 
 	regs->flags = (regs->flags & ~FIX_EFLAGS) | (sc.flags & FIX_EFLAGS);
 	/* disable syscall checks */
@@ -522,10 +524,15 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
 	 * a trampoline.)  So we do our best: if the old SS was valid,
 	 * we keep it.  Otherwise we replace it.
 	 */
-	regs->cs = __USER_CS;
+	if (!is_ukl_thread()) {
+		regs->cs = __USER_CS;
 
-	if (unlikely(regs->ss != __USER_DS))
-		force_valid_ss(regs);
+		if (unlikely(regs->ss != __USER_DS))
+			force_valid_ss(regs);
+	} else {
+		regs->cs = 0xC3;
+		regs->ss = __KERNEL_DS;
+	}
 
 	return 0;
 
@@ -662,7 +669,10 @@ SYSCALL_DEFINE0(rt_sigreturn)
 	sigset_t set;
 	unsigned long uc_flags;
 
-	frame = (struct rt_sigframe __user *)(regs->sp - sizeof(long));
+	if (is_ukl_thread())
+		frame = (struct rt_sigframe __user *)(regs->sp + sizeof(long));
+	else
+		frame = (struct rt_sigframe __user *)(regs->sp - sizeof(long));
 	if (!access_ok(frame, sizeof(*frame)))
 		goto badframe;
 	if (__get_user(*(__u64 *)&set, (__u64 __user *)&frame->uc.uc_sigmask))
-- 
2.21.3


  parent reply	other threads:[~2022-10-03 22:22 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-03 22:21 [RFC UKL 00/10] Unikernel Linux (UKL) Ali Raza
2022-10-03 22:21 ` [RFC UKL 01/10] kbuild: Add sections and symbols to linker script for UKL support Ali Raza
2022-10-03 22:21 ` [RFC UKL 02/10] x86/boot: Load the PT_TLS segment for Unikernel configs Ali Raza
2022-10-04 17:30   ` Andy Lutomirski
2022-10-06 21:00     ` Ali Raza
2022-10-03 22:21 ` [RFC UKL 03/10] sched: Add task_struct tracking of kernel or application execution Ali Raza
2022-10-03 22:21 ` [RFC UKL 04/10] x86/entry: Create alternate entry path for system calls Ali Raza
2022-10-04 17:43   ` Andy Lutomirski
2022-10-06 21:12     ` Ali Raza
2022-10-03 22:21 ` [RFC UKL 05/10] x86/uaccess: Make access_ok UKL aware Ali Raza
2022-10-04 17:36   ` Andy Lutomirski
2022-10-06 21:16     ` Ali Raza
2022-10-03 22:21 ` [RFC UKL 06/10] x86/fault: Skip checking kernel mode access to user address space for UKL Ali Raza
2022-10-03 22:21 ` Ali Raza [this message]
2022-10-04 17:34   ` [RFC UKL 07/10] x86/signal: Adjust signal handler register values and return frame Andy Lutomirski
2022-10-06 21:20     ` Ali Raza
2022-10-03 22:21 ` [RFC UKL 08/10] exec: Make exec path for starting UKL application Ali Raza
2022-10-03 22:21 ` [RFC UKL 09/10] exec: Give userspace a method for starting UKL process Ali Raza
2022-10-04 17:35   ` Andy Lutomirski
2022-10-06 21:25     ` Ali Raza
2022-10-03 22:21 ` [RFC UKL 10/10] Kconfig: Add config option for enabling and sample for testing UKL Ali Raza
2022-10-04  2:11   ` Bagas Sanjaya
2022-10-06 21:28     ` Ali Raza
2022-10-07 10:21       ` Masahiro Yamada
2022-10-13 17:08         ` Ali Raza
2022-10-06 21:27 ` [RFC UKL 00/10] Unikernel Linux (UKL) H. Peter Anvin

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