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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Ondrej Zary <linux@zary.sk>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	stable@kernel.org
Subject: [PATCH 5.10 12/21] x86/iopl: Fake iopl(3) CLI/STI usage
Date: Fri, 19 Nov 2021 18:37:47 +0100	[thread overview]
Message-ID: <20211119171444.279834831@linuxfoundation.org> (raw)
In-Reply-To: <20211119171443.892729043@linuxfoundation.org>

From: Peter Zijlstra <peterz@infradead.org>

commit b968e84b509da593c50dc3db679e1d33de701f78 upstream.

Since commit c8137ace5638 ("x86/iopl: Restrict iopl() permission
scope") it's possible to emulate iopl(3) using ioperm(), except for
the CLI/STI usage.

Userspace CLI/STI usage is very dubious (read broken), since any
exception taken during that window can lead to rescheduling anyway (or
worse). The IOPL(2) manpage even states that usage of CLI/STI is highly
discouraged and might even crash the system.

Of course, that won't stop people and HP has the dubious honour of
being the first vendor to be found using this in their hp-health
package.

In order to enable this 'software' to still 'work', have the #GP treat
the CLI/STI instructions as NOPs when iopl(3). Warn the user that
their program is doing dubious things.

Fixes: a24ca9976843 ("x86/iopl: Remove legacy IOPL option")
Reported-by: Ondrej Zary <linux@zary.sk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org # v5.5+
Link: https://lkml.kernel.org/r/20210918090641.GD5106@worktop.programming.kicks-ass.net
Signed-off-by: Ondrej Zary <linux@zary.sk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/include/asm/insn-eval.h |    1 +
 arch/x86/include/asm/processor.h |    1 +
 arch/x86/kernel/process.c        |    1 +
 arch/x86/kernel/traps.c          |   34 ++++++++++++++++++++++++++++++++++
 arch/x86/lib/insn-eval.c         |    2 +-
 5 files changed, 38 insertions(+), 1 deletion(-)

--- a/arch/x86/include/asm/insn-eval.h
+++ b/arch/x86/include/asm/insn-eval.h
@@ -21,6 +21,7 @@ int insn_get_modrm_rm_off(struct insn *i
 int insn_get_modrm_reg_off(struct insn *insn, struct pt_regs *regs);
 unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx);
 int insn_get_code_seg_params(struct pt_regs *regs);
+unsigned long insn_get_effective_ip(struct pt_regs *regs);
 int insn_fetch_from_user(struct pt_regs *regs,
 			 unsigned char buf[MAX_INSN_SIZE]);
 int insn_fetch_from_user_inatomic(struct pt_regs *regs,
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -534,6 +534,7 @@ struct thread_struct {
 	 */
 	unsigned long		iopl_emul;
 
+	unsigned int		iopl_warn:1;
 	unsigned int		sig_on_uaccess_err:1;
 
 	/* Floating point and extended processor state */
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -138,6 +138,7 @@ int copy_thread(unsigned long clone_flag
 	frame->ret_addr = (unsigned long) ret_from_fork;
 	p->thread.sp = (unsigned long) fork_frame;
 	p->thread.io_bitmap = NULL;
+	p->thread.iopl_warn = 0;
 	memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
 
 #ifdef CONFIG_X86_64
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -523,6 +523,37 @@ static enum kernel_gp_hint get_kernel_gp
 
 #define GPFSTR "general protection fault"
 
+static bool fixup_iopl_exception(struct pt_regs *regs)
+{
+	struct thread_struct *t = &current->thread;
+	unsigned char byte;
+	unsigned long ip;
+
+	if (!IS_ENABLED(CONFIG_X86_IOPL_IOPERM) || t->iopl_emul != 3)
+		return false;
+
+	ip = insn_get_effective_ip(regs);
+	if (!ip)
+		return false;
+
+	if (get_user(byte, (const char __user *)ip))
+		return false;
+
+	if (byte != 0xfa && byte != 0xfb)
+		return false;
+
+	if (!t->iopl_warn && printk_ratelimit()) {
+		pr_err("%s[%d] attempts to use CLI/STI, pretending it's a NOP, ip:%lx",
+		       current->comm, task_pid_nr(current), ip);
+		print_vma_addr(KERN_CONT " in ", ip);
+		pr_cont("\n");
+		t->iopl_warn = 1;
+	}
+
+	regs->ip += 1;
+	return true;
+}
+
 DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
 {
 	char desc[sizeof(GPFSTR) + 50 + 2*sizeof(unsigned long) + 1] = GPFSTR;
@@ -548,6 +579,9 @@ DEFINE_IDTENTRY_ERRORCODE(exc_general_pr
 	tsk = current;
 
 	if (user_mode(regs)) {
+		if (fixup_iopl_exception(regs))
+			goto exit;
+
 		tsk->thread.error_code = error_code;
 		tsk->thread.trap_nr = X86_TRAP_GP;
 
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -1415,7 +1415,7 @@ void __user *insn_get_addr_ref(struct in
 	}
 }
 
-static unsigned long insn_get_effective_ip(struct pt_regs *regs)
+unsigned long insn_get_effective_ip(struct pt_regs *regs)
 {
 	unsigned long seg_base = 0;
 



  parent reply	other threads:[~2021-11-19 17:38 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-19 17:37 [PATCH 5.10 00/21] 5.10.81-rc1 review Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 01/21] fortify: Explicitly disable Clang support Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 02/21] block: Add a helper to validate the block size Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 03/21] loop: Use blk_validate_block_size() to validate " Greg Kroah-Hartman
2021-11-19 21:45   ` Pavel Machek
2021-11-20  7:39     ` Greg Kroah-Hartman
2021-11-21 16:59       ` Pavel Machek
2021-11-19 17:37 ` [PATCH 5.10 04/21] bootconfig: init: Fix memblock leak in xbc_make_cmdline() Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 05/21] net: stmmac: add clocks management for gmac driver Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 06/21] net: stmmac: platform: fix build error with !CONFIG_PM_SLEEP Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 07/21] net: stmmac: fix missing unlock on error in stmmac_suspend() Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 08/21] net: stmmac: fix system hang if change mac address after interface ifdown Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 09/21] net: stmmac: fix issue where clk is being unprepared twice Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 10/21] net: stmmac: dwmac-rk: fix unbalanced pm_runtime_enable warnings Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 11/21] arm64: vdso32: suppress error message for make mrproper Greg Kroah-Hartman
2021-11-19 21:47   ` Pavel Machek
2021-11-19 22:24     ` Nick Desaulniers
2021-11-19 22:30       ` Nick Desaulniers
2021-11-21  7:48       ` Greg Kroah-Hartman
2021-11-19 17:37 ` Greg Kroah-Hartman [this message]
2021-11-19 17:37 ` [PATCH 5.10 13/21] parisc/entry: fix trace test in syscall exit path Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 14/21] PCI/MSI: Destroy sysfs before freeing entries Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 15/21] PCI/MSI: Deal with devices lying about their MSI mask capability Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 16/21] PCI: Add MSI masking quirk for Nvidia ION AHCI Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 17/21] erofs: remove the occupied parameter from z_erofs_pagevec_enqueue() Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 18/21] erofs: fix unsafe pagevec reuse of hooked pclusters Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 19/21] scripts/lld-version.sh: Rewrite based on upstream ld-version.sh Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 20/21] perf/core: Avoid put_page() when GUP fails Greg Kroah-Hartman
2021-11-19 17:37 ` [PATCH 5.10 21/21] thermal: Fix NULL pointer dereferences in of_thermal_ functions Greg Kroah-Hartman
2021-11-19 18:46 ` [PATCH 5.10 00/21] 5.10.81-rc1 review Florian Fainelli
2021-11-19 19:46 ` Fox Chen
2021-11-20  0:49 ` Shuah Khan
2021-11-20  7:28 ` Pavel Machek
2021-11-20 15:21 ` Sudip Mukherjee
2021-11-20 15:27 ` Daniel Díaz
2021-11-20 16:06   ` Naresh Kamboju
2021-11-21  7:49     ` Greg Kroah-Hartman
2021-11-20 16:52 ` Guenter Roeck
2021-11-22  2:48 ` Samuel Zou

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