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kernel
os
linux
um: Add helper functions to get/set state for SECCOMP
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>
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20250602130052.545733-4-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
authored by
Benjamin Berg
and committed by
Johannes Berg
b1e1bd2e
dac494bf
+283
-20
+217
-1
arch/x86/um/os-Linux/mcontext.c
+217
-1
arch/x86/um/os-Linux/mcontext.c
···
1
1
// SPDX-License-Identifier: GPL-2.0
2
-
#include <sys/ucontext.h>
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#define __FRAME_OFFSETS
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#include <linux/errno.h>
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#include <linux/string.h>
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#include <sys/ucontext.h>
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#include <asm/ptrace.h>
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#include <asm/sigcontext.h>
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#include <sysdep/ptrace.h>
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#include <sysdep/mcontext.h>
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#include <arch.h>
···
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COPY2(UESP, ESP); /* sic */
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COPY(EBX); COPY(EDX); COPY(ECX); COPY(EAX);
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COPY(EIP); COPY_SEG_CPL3(CS); COPY(EFL); COPY_SEG_CPL3(SS);
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#undef COPY2
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#undef COPY
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#undef COPY_SEG
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#undef COPY_SEG_CPL3
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#else
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#define COPY2(X,Y) regs->gp[X/sizeof(unsigned long)] = mc->gregs[REG_##Y]
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#define COPY(X) regs->gp[X/sizeof(unsigned long)] = mc->gregs[REG_##X]
···
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COPY2(EFLAGS, EFL);
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COPY2(CS, CSGSFS);
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regs->gp[SS / sizeof(unsigned long)] = mc->gregs[REG_CSGSFS] >> 48;
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#undef COPY2
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#undef COPY
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#endif
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}
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···
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#else
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mc->gregs[REG_RIP] = (unsigned long)target;
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#endif
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}
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+
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/* Same thing, but the copy macros are turned around. */
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void get_mc_from_regs(struct uml_pt_regs *regs, mcontext_t *mc, int single_stepping)
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{
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#ifdef __i386__
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#define COPY2(X,Y) mc->gregs[REG_##Y] = regs->gp[X]
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#define COPY(X) mc->gregs[REG_##X] = regs->gp[X]
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#define COPY_SEG(X) mc->gregs[REG_##X] = regs->gp[X] & 0xffff;
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#define COPY_SEG_CPL3(X) mc->gregs[REG_##X] = (regs->gp[X] & 0xffff) | 3;
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COPY_SEG(GS); COPY_SEG(FS); COPY_SEG(ES); COPY_SEG(DS);
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COPY(EDI); COPY(ESI); COPY(EBP);
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COPY2(UESP, ESP); /* sic */
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COPY(EBX); COPY(EDX); COPY(ECX); COPY(EAX);
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COPY(EIP); COPY_SEG_CPL3(CS); COPY(EFL); COPY_SEG_CPL3(SS);
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#else
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#define COPY2(X,Y) mc->gregs[REG_##Y] = regs->gp[X/sizeof(unsigned long)]
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#define COPY(X) mc->gregs[REG_##X] = regs->gp[X/sizeof(unsigned long)]
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COPY(R8); COPY(R9); COPY(R10); COPY(R11);
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COPY(R12); COPY(R13); COPY(R14); COPY(R15);
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COPY(RDI); COPY(RSI); COPY(RBP); COPY(RBX);
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COPY(RDX); COPY(RAX); COPY(RCX); COPY(RSP);
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COPY(RIP);
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COPY2(EFLAGS, EFL);
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mc->gregs[REG_CSGSFS] = mc->gregs[REG_CSGSFS] & 0xffffffffffffl;
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mc->gregs[REG_CSGSFS] |= (regs->gp[SS / sizeof(unsigned long)] & 0xffff) << 48;
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#endif
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if (single_stepping)
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mc->gregs[REG_EFL] |= X86_EFLAGS_TF;
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else
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mc->gregs[REG_EFL] &= ~X86_EFLAGS_TF;
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}
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#ifdef CONFIG_X86_32
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struct _xstate_64 {
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struct _fpstate_64 fpstate;
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struct _header xstate_hdr;
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struct _ymmh_state ymmh;
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/* New processor state extensions go here: */
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};
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/* Not quite the right structures as these contain more information */
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int um_i387_from_fxsr(struct _fpstate_32 *i387,
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const struct _fpstate_64 *fxsave);
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int um_fxsr_from_i387(struct _fpstate_64 *fxsave,
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const struct _fpstate_32 *from);
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#else
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#define _xstate_64 _xstate
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#endif
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static struct _fpstate *get_fpstate(struct stub_data *data,
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mcontext_t *mcontext,
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int *fp_size)
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{
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struct _fpstate *res;
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/* Assume floating point registers are on the same page */
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res = (void *)(((unsigned long)mcontext->fpregs &
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(UM_KERN_PAGE_SIZE - 1)) +
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(unsigned long)&data->sigstack[0]);
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if ((void *)res + sizeof(struct _fpstate) >
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(void *)data->sigstack + sizeof(data->sigstack))
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return NULL;
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if (res->sw_reserved.magic1 != FP_XSTATE_MAGIC1) {
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*fp_size = sizeof(struct _fpstate);
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} else {
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char *magic2_addr;
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magic2_addr = (void *)res;
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magic2_addr += res->sw_reserved.extended_size;
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magic2_addr -= FP_XSTATE_MAGIC2_SIZE;
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/* We still need to be within our stack */
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if ((void *)magic2_addr >
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(void *)data->sigstack + sizeof(data->sigstack))
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return NULL;
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/* If we do not read MAGIC2, then we did something wrong */
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if (*(__u32 *)magic2_addr != FP_XSTATE_MAGIC2)
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return NULL;
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/* Remove MAGIC2 from the size, we do not save/restore it */
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*fp_size = res->sw_reserved.extended_size -
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FP_XSTATE_MAGIC2_SIZE;
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}
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return res;
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}
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int get_stub_state(struct uml_pt_regs *regs, struct stub_data *data,
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unsigned long *fp_size_out)
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{
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mcontext_t *mcontext;
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struct _fpstate *fpstate_stub;
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struct _xstate_64 *xstate_stub;
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int fp_size, xstate_size;
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/* mctx_offset is verified by wait_stub_done_seccomp */
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mcontext = (void *)&data->sigstack[data->mctx_offset];
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get_regs_from_mc(regs, mcontext);
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fpstate_stub = get_fpstate(data, mcontext, &fp_size);
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if (!fpstate_stub)
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return -EINVAL;
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#ifdef CONFIG_X86_32
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xstate_stub = (void *)&fpstate_stub->_fxsr_env;
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xstate_size = fp_size - offsetof(struct _fpstate_32, _fxsr_env);
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#else
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xstate_stub = (void *)fpstate_stub;
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xstate_size = fp_size;
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#endif
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if (fp_size_out)
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*fp_size_out = xstate_size;
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if (xstate_size > host_fp_size)
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return -ENOSPC;
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memcpy(®s->fp, xstate_stub, xstate_size);
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/* We do not need to read the x86_64 FS_BASE/GS_BASE registers as
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* we do not permit userspace to set them directly.
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*/
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#ifdef CONFIG_X86_32
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/* Read the i387 legacy FP registers */
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if (um_fxsr_from_i387((void *)®s->fp, fpstate_stub))
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return -EINVAL;
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#endif
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return 0;
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}
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/* Copied because we cannot include regset.h here. */
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struct task_struct;
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struct user_regset;
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struct membuf {
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void *p;
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size_t left;
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};
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int fpregs_legacy_get(struct task_struct *target,
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const struct user_regset *regset,
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struct membuf to);
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int set_stub_state(struct uml_pt_regs *regs, struct stub_data *data,
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int single_stepping)
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{
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mcontext_t *mcontext;
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struct _fpstate *fpstate_stub;
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struct _xstate_64 *xstate_stub;
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int fp_size, xstate_size;
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/* mctx_offset is verified by wait_stub_done_seccomp */
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mcontext = (void *)&data->sigstack[data->mctx_offset];
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if ((unsigned long)mcontext < (unsigned long)data->sigstack ||
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(unsigned long)mcontext >
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(unsigned long) data->sigstack +
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sizeof(data->sigstack) - sizeof(*mcontext))
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return -EINVAL;
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get_mc_from_regs(regs, mcontext, single_stepping);
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fpstate_stub = get_fpstate(data, mcontext, &fp_size);
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if (!fpstate_stub)
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return -EINVAL;
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#ifdef CONFIG_X86_32
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xstate_stub = (void *)&fpstate_stub->_fxsr_env;
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xstate_size = fp_size - offsetof(struct _fpstate_32, _fxsr_env);
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#else
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xstate_stub = (void *)fpstate_stub;
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xstate_size = fp_size;
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#endif
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memcpy(fpstate_stub, ®s->fp, fp_size);
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#ifdef __i386__
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/*
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* On x86, the GDT entries are updated by arch_set_tls.
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*/
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/* Store the i387 legacy FP registers which the host will use */
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if (um_i387_from_fxsr(fpstate_stub, (void *)®s->fp))
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return -EINVAL;
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#else
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/*
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* On x86_64, we need to sync the FS_BASE/GS_BASE registers using the
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* arch specific data.
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*/
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if (data->arch_data.fs_base != regs->gp[FS_BASE / sizeof(unsigned long)]) {
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data->arch_data.fs_base = regs->gp[FS_BASE / sizeof(unsigned long)];
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data->arch_data.sync |= STUB_SYNC_FS_BASE;
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}
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if (data->arch_data.gs_base != regs->gp[GS_BASE / sizeof(unsigned long)]) {
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data->arch_data.gs_base = regs->gp[GS_BASE / sizeof(unsigned long)];
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data->arch_data.sync |= STUB_SYNC_GS_BASE;
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}
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#endif
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return 0;
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}
+57
-19
arch/x86/um/ptrace.c
+57
-19
arch/x86/um/ptrace.c
···
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return tmp;
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}
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static inline unsigned long twd_fxsr_to_i387(struct user_fxsr_struct *fxsave)
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static inline unsigned long
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twd_fxsr_to_i387(const struct user_fxsr_struct *fxsave)
29
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{
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struct _fpxreg *st = NULL;
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unsigned long twd = (unsigned long) fxsave->twd;
···
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return ret;
71
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}
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/* Get/set the old 32bit i387 registers (pre-FPX) */
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static int fpregs_legacy_get(struct task_struct *target,
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const struct user_regset *regset,
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struct membuf to)
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/*
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* Get/set the old 32bit i387 registers (pre-FPX)
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*
75
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* We provide simple wrappers for mcontext.c, they are only defined locally
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* because mcontext.c is userspace facing and needs to a different definition
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* of the structures.
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*/
79
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static int _um_i387_from_fxsr(struct membuf to,
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const struct user_fxsr_struct *fxsave)
77
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{
78
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struct user_fxsr_struct *fxsave = (void *)target->thread.regs.regs.fp;
79
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int i;
80
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81
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membuf_store(&to, (unsigned long)fxsave->cwd | 0xffff0000ul);
···
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return 0;
97
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}
98
93
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-
static int fpregs_legacy_set(struct task_struct *target,
94
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int um_i387_from_fxsr(struct user_i387_struct *i387,
95
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const struct user_fxsr_struct *fxsave);
96
+
97
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int um_i387_from_fxsr(struct user_i387_struct *i387,
98
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const struct user_fxsr_struct *fxsave)
99
+
{
100
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struct membuf to = {
101
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.p = i387,
102
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.left = sizeof(*i387),
103
+
};
104
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105
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return _um_i387_from_fxsr(to, fxsave);
106
+
}
107
+
108
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static int fpregs_legacy_get(struct task_struct *target,
100
109
const struct user_regset *regset,
101
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unsigned int pos, unsigned int count,
102
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const void *kbuf, const void __user *ubuf)
110
+
struct membuf to)
103
111
{
104
112
struct user_fxsr_struct *fxsave = (void *)target->thread.regs.regs.fp;
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const struct user_i387_struct *from;
106
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struct user_i387_struct buf;
107
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int i;
108
113
109
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if (ubuf) {
110
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if (copy_from_user(&buf, ubuf, sizeof(buf)))
111
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return -EFAULT;
112
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from = &buf;
113
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} else {
114
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from = kbuf;
115
-
}
114
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return _um_i387_from_fxsr(to, fxsave);
115
+
}
116
+
117
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int um_fxsr_from_i387(struct user_fxsr_struct *fxsave,
118
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const struct user_i387_struct *from);
119
+
120
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int um_fxsr_from_i387(struct user_fxsr_struct *fxsave,
121
+
const struct user_i387_struct *from)
122
+
{
123
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int i;
116
124
117
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fxsave->cwd = (unsigned short)(from->cwd & 0xffff);
118
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fxsave->swd = (unsigned short)(from->swd & 0xffff);
···
142
124
}
143
125
144
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return 0;
127
+
}
128
+
129
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static int fpregs_legacy_set(struct task_struct *target,
130
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const struct user_regset *regset,
131
+
unsigned int pos, unsigned int count,
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const void *kbuf, const void __user *ubuf)
133
+
{
134
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struct user_fxsr_struct *fxsave = (void *)target->thread.regs.regs.fp;
135
+
const struct user_i387_struct *from;
136
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struct user_i387_struct buf;
137
+
138
+
if (ubuf) {
139
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if (copy_from_user(&buf, ubuf, sizeof(buf)))
140
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return -EFAULT;
141
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from = &buf;
142
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} else {
143
+
from = kbuf;
144
+
}
145
+
146
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return um_fxsr_from_i387(fxsave, &buf);
145
147
}
146
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#endif
147
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