diff mbox series

[v2,24/28] um: Add helper functions to get/set state for SECCOMP

Message ID 20221122100759.208290-25-benjamin@sipsolutions.net
State Under Review
Delegated to: Richard Weinberger
Headers show
Series Implement SECCOMP based userland | expand

Commit Message

Benjamin Berg Nov. 22, 2022, 10:07 a.m. UTC 
From: Benjamin Berg <benjamin@sipsolutions.net>

When not using ptrace, we need to both save and restore registers
through the mcontext as provided by the host kernel to our signal
handlers.

Add corresponding functions to store the state to an mcontext and
helpers to access the mcontext of the subprocess through the stub data.

Signed-off-by: Benjamin Berg <benjamin@sipsolutions.net>
---
 arch/um/include/shared/common-offsets.h |   9 +-
 arch/x86/um/os-Linux/mcontext.c         | 150 +++++++++++++++++++++++-
 arch/x86/um/shared/sysdep/mcontext.h    |   9 ++
 3 files changed, 166 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/arch/um/include/shared/common-offsets.h b/arch/um/include/shared/common-offsets.h
index 579ed946a3a9..307dba626001 100644
--- a/arch/um/include/shared/common-offsets.h
+++ b/arch/um/include/shared/common-offsets.h
@@ -28,4 +28,11 @@  DEFINE(UML_CONFIG_64BIT, CONFIG_64BIT);
 #ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
 DEFINE(UML_CONFIG_UML_TIME_TRAVEL_SUPPORT, CONFIG_UML_TIME_TRAVEL_SUPPORT);
 #endif
-
+#ifdef CONFIG_UML_SECCOMP
+DEFINE(UM_FPSTATE_EXTENDED_SIZE,
+       offsetof(struct _fpstate, sw_reserved)
+       + offsetof(struct _fpx_sw_bytes, extended_size));
+DEFINE(UM_FPSTATE_XSTATE_SIZE,
+       offsetof(struct _fpstate, sw_reserved)
+       + offsetof(struct _fpx_sw_bytes, xstate_size));
+#endif
diff --git a/arch/x86/um/os-Linux/mcontext.c b/arch/x86/um/os-Linux/mcontext.c
index 81b9d1f9f4e6..aabebe58fb25 100644
--- a/arch/x86/um/os-Linux/mcontext.c
+++ b/arch/x86/um/os-Linux/mcontext.c
@@ -1,8 +1,12 @@ 
 // SPDX-License-Identifier: GPL-2.0
-#include <sys/ucontext.h>
 #define __FRAME_OFFSETS
 #include <asm/ptrace.h>
 #include <sysdep/ptrace.h>
+#include <string.h>
+#include <signal.h>
+#include <sysdep/mcontext.h>
+#include <linux/errno.h>
+#include <generated/asm-offsets.h>
 
 void get_regs_from_mc(struct uml_pt_regs *regs, mcontext_t *mc)
 {
@@ -16,6 +20,10 @@  void get_regs_from_mc(struct uml_pt_regs *regs, mcontext_t *mc)
 	COPY2(UESP, ESP); /* sic */
 	COPY(EBX); COPY(EDX); COPY(ECX); COPY(EAX);
 	COPY(EIP); COPY_SEG_CPL3(CS); COPY(EFL); COPY_SEG_CPL3(SS);
+#undef COPY2
+#undef COPY
+#undef COPY_SEG
+#undef COPY_SEG_CPL3
 #else
 #define COPY2(X,Y) regs->gp[X/sizeof(unsigned long)] = mc->gregs[REG_##Y]
 #define COPY(X) regs->gp[X/sizeof(unsigned long)] = mc->gregs[REG_##X]
@@ -27,5 +35,145 @@  void get_regs_from_mc(struct uml_pt_regs *regs, mcontext_t *mc)
 	COPY2(EFLAGS, EFL);
 	COPY2(CS, CSGSFS);
 	regs->gp[SS / sizeof(unsigned long)] = mc->gregs[REG_CSGSFS] >> 48;
+#undef COPY2
+#undef COPY
 #endif
 }
+
+#ifdef CONFIG_UML_SECCOMP
+/* Same thing, but the copy macros are turned around. */
+void get_mc_from_regs(struct uml_pt_regs *regs, mcontext_t *mc, int single_stepping)
+{
+#ifdef __i386__
+#define COPY2(X,Y) mc->gregs[REG_##Y] = regs->gp[X]
+#define COPY(X) mc->gregs[REG_##X] = regs->gp[X]
+#define COPY_SEG(X) mc->gregs[REG_##X] = mc->gregs[REG_##X] & 0xffff;
+#define COPY_SEG_CPL3(X) mc->gregs[REG_##X] = (regs->gp[X] & 0xffff) | 3;
+	COPY_SEG(GS); COPY_SEG(FS); COPY_SEG(ES); COPY_SEG(DS);
+	COPY(EDI); COPY(ESI); COPY(EBP);
+	COPY2(UESP, ESP); /* sic */
+	COPY(EBX); COPY(EDX); COPY(ECX); COPY(EAX);
+	COPY(EIP); COPY_SEG_CPL3(CS); COPY(EFL); COPY_SEG_CPL3(SS);
+#else
+#define COPY2(X,Y) mc->gregs[REG_##Y] = regs->gp[X/sizeof(unsigned long)]
+#define COPY(X) mc->gregs[REG_##X] = regs->gp[X/sizeof(unsigned long)]
+	COPY(R8); COPY(R9); COPY(R10); COPY(R11);
+	COPY(R12); COPY(R13); COPY(R14); COPY(R15);
+	COPY(RDI); COPY(RSI); COPY(RBP); COPY(RBX);
+	COPY(RDX); COPY(RAX); COPY(RCX); COPY(RSP);
+	COPY(RIP);
+	COPY2(EFLAGS, EFL);
+	mc->gregs[REG_CSGSFS] = mc->gregs[REG_CSGSFS] & 0xffffffffffffl;
+	mc->gregs[REG_CSGSFS] |= (regs->gp[SS / sizeof(unsigned long)] & 0xffff) << 48;
+#endif
+
+	if (single_stepping)
+		mc->gregs[REG_EFL] |= X86_EFLAGS_TF;
+	else
+		mc->gregs[REG_EFL] &= ~X86_EFLAGS_TF;
+}
+
+int get_stub_state(struct uml_pt_regs *regs, struct stub_data *data)
+{
+	mcontext_t *mcontext;
+	unsigned long fp_regs;
+	int fp_size;
+
+	/* mctx_offset is verified by wait_stub_done_seccomp */
+	mcontext = (void *)&data->sigstack[data->mctx_offset];
+
+	get_regs_from_mc(regs, mcontext);
+
+	/* Assume floating point registers are on the same page */
+	fp_regs = (((unsigned long)mcontext->fpregs &
+		    (UM_KERN_PAGE_SIZE - 1)) +
+		   (unsigned long)&data->sigstack[0]);
+
+	/* Use extended_size, but never touch the trailing magic
+	 * (as it may not fit our internal storage)
+	 */
+	fp_size = *(int *)(fp_regs + UM_FPSTATE_EXTENDED_SIZE)
+		  - FP_XSTATE_MAGIC2_SIZE;
+
+	if (fp_size > sizeof(regs->fp))
+		return -ENOSPC;
+
+	if (fp_regs + fp_size > (unsigned long)data->sigstack +
+				sizeof(data->sigstack))
+		return -EINVAL;
+
+	memcpy(&regs->fp, (void *)fp_regs, fp_size);
+
+	/* We do not need to read the x86_64 FS_BASE/GS_BASE registers as
+	 * we do not permit userspace to set them directly.
+	 */
+
+	return 0;
+}
+
+int set_stub_state(struct uml_pt_regs *regs, struct stub_data *data,
+		   int single_stepping)
+{
+	mcontext_t *mcontext;
+	unsigned long fp_regs;
+	int fp_size;
+	int fp_size_stub;
+
+	/* mctx_offset is verified by wait_stub_done_seccomp */
+	mcontext = (void *)&data->sigstack[data->mctx_offset];
+
+	if ((unsigned long)mcontext < (unsigned long)data->sigstack ||
+	    (unsigned long)mcontext >
+			(unsigned long) data->sigstack +
+			sizeof(data->sigstack) - sizeof(*mcontext))
+		return -EINVAL;
+
+	get_mc_from_regs(regs, mcontext, single_stepping);
+
+	/* Assume floating point registers are on the same page */
+	fp_regs = (((unsigned long)mcontext->fpregs &
+		    (UM_KERN_PAGE_SIZE - 1)) +
+		   (unsigned long)&data->sigstack[0]);
+
+	/* Use extended_size, but never touch the trailing magic
+	 * (as it may not fit our internal storage)
+	 */
+	fp_size = *(int *)((unsigned long) &regs->fp +
+			   UM_FPSTATE_EXTENDED_SIZE) -
+		  FP_XSTATE_MAGIC2_SIZE;
+	fp_size_stub = *(int *)(fp_regs + UM_FPSTATE_EXTENDED_SIZE) -
+		       FP_XSTATE_MAGIC2_SIZE;
+
+	/* Can we fit it, or would we need an alternative memory location? */
+	if (fp_size > fp_size_stub)
+		return -ENOSPC;
+
+	if (fp_regs + fp_size > (unsigned long)data->sigstack +
+				sizeof(data->sigstack))
+		return -EINVAL;
+
+	memcpy((void *) fp_regs, &regs->fp, fp_size);
+
+#ifdef __i386__
+	/*
+	 * On x86, we need to sync the GDT entries for the thread local storage.
+	 */
+	#error "Not implemented"
+#else
+	/*
+	 * On x86_64, we need to sync the FS_BASE/GS_BASE registers using the
+	 * arch specific data.
+	 */
+	if (data->arch_data.fs_base != regs->gp[FS_BASE / sizeof(unsigned long)]) {
+		data->arch_data.fs_base = regs->gp[FS_BASE / sizeof(unsigned long)];
+		data->arch_data.sync |= STUB_SYNC_FS_BASE;
+	}
+	if (data->arch_data.gs_base != regs->gp[GS_BASE / sizeof(unsigned long)]) {
+		data->arch_data.gs_base = regs->gp[GS_BASE / sizeof(unsigned long)];
+		data->arch_data.sync |= STUB_SYNC_GS_BASE;
+	}
+#endif
+
+	return 0;
+}
+#endif
diff --git a/arch/x86/um/shared/sysdep/mcontext.h b/arch/x86/um/shared/sysdep/mcontext.h
index b724c54da316..3ea6da0dbe9d 100644
--- a/arch/x86/um/shared/sysdep/mcontext.h
+++ b/arch/x86/um/shared/sysdep/mcontext.h
@@ -6,7 +6,16 @@ 
 #ifndef __SYS_SIGCONTEXT_X86_H
 #define __SYS_SIGCONTEXT_X86_H
 
+#include <linux/kconfig.h>
+#include <stub-data.h>
+
 extern void get_regs_from_mc(struct uml_pt_regs *, mcontext_t *);
+extern void get_mc_from_regs(struct uml_pt_regs *regs, mcontext_t *mc,
+			     int single_stepping);
+
+extern int get_stub_state(struct uml_pt_regs *regs, struct stub_data *data);
+extern int set_stub_state(struct uml_pt_regs *regs, struct stub_data *data,
+			  int single_stepping);
 
 #ifdef __i386__