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x86/insn-eval: Add support for 64-bit kernel mode 

To support evaluating 64-bit kernel mode instructions:

* Replace existing checks for user_64bit_mode() with a new helper that
checks whether code is being executed in either 64-bit kernel mode or
64-bit user mode.

* Select the GS base depending on whether the instruction is being
evaluated in kernel mode.

Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: kasan-dev@googlegroups.com
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20191218231150.12139-1-jannh@google.com
This commit is contained in:
Jann Horn 2019-12-19 00:11:47 +01:00 committed by Borislav Petkov
parent fd6988496e
commit 7be4412721
2 changed files with 28 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
arch/x86/include/asm/ptrace.h
View File

@ -159,6 +159,19 @@ static inline bool user_64bit_mode(struct pt_regs *regs)
#endif
}
/*
* Determine whether the register set came from any context that is running in
* 64-bit mode.
*/
static inline bool any_64bit_mode(struct pt_regs *regs)
{
#ifdef CONFIG_X86_64
return !user_mode(regs) || user_64bit_mode(regs);
#else
return false;
#endif
}
#ifdef CONFIG_X86_64
#define current_user_stack_pointer() current_pt_regs()->sp
#define compat_user_stack_pointer() current_pt_regs()->sp

26
arch/x86/lib/insn-eval.c
View File

@ -155,7 +155,7 @@ static bool check_seg_overrides(struct insn *insn, int regoff)
*/
static int resolve_default_seg(struct insn *insn, struct pt_regs *regs, int off)
{
if (user_64bit_mode(regs))
if (any_64bit_mode(regs))
return INAT_SEG_REG_IGNORE;
/*
* Resolve the default segment register as described in Section 3.7.4
@ -266,7 +266,7 @@ static int resolve_seg_reg(struct insn *insn, struct pt_regs *regs, int regoff)
* which may be invalid at this point.
*/
if (regoff == offsetof(struct pt_regs, ip)) {
if (user_64bit_mode(regs))
if (any_64bit_mode(regs))
return INAT_SEG_REG_IGNORE;
else
return INAT_SEG_REG_CS;
@ -289,7 +289,7 @@ static int resolve_seg_reg(struct insn *insn, struct pt_regs *regs, int regoff)
* In long mode, segment override prefixes are ignored, except for
* overrides for FS and GS.
*/
if (user_64bit_mode(regs)) {
if (any_64bit_mode(regs)) {
if (idx != INAT_SEG_REG_FS &&
idx != INAT_SEG_REG_GS)
idx = INAT_SEG_REG_IGNORE;
@ -646,23 +646,27 @@ unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx)
*/
return (unsigned long)(sel << 4);
if (user_64bit_mode(regs)) {
if (any_64bit_mode(regs)) {
/*
* Only FS or GS will have a base address, the rest of
* the segments' bases are forced to 0.
*/
unsigned long base;
if (seg_reg_idx == INAT_SEG_REG_FS)
if (seg_reg_idx == INAT_SEG_REG_FS) {
rdmsrl(MSR_FS_BASE, base);
else if (seg_reg_idx == INAT_SEG_REG_GS)
} else if (seg_reg_idx == INAT_SEG_REG_GS) {
/*
* swapgs was called at the kernel entry point. Thus,
* MSR_KERNEL_GS_BASE will have the user-space GS base.
*/
rdmsrl(MSR_KERNEL_GS_BASE, base);
else
if (user_mode(regs))
rdmsrl(MSR_KERNEL_GS_BASE, base);
else
rdmsrl(MSR_GS_BASE, base);
} else {
base = 0;
}
return base;
}
@ -703,7 +707,7 @@ static unsigned long get_seg_limit(struct pt_regs *regs, int seg_reg_idx)
if (sel < 0)
return 0;
if (user_64bit_mode(regs) || v8086_mode(regs))
if (any_64bit_mode(regs) || v8086_mode(regs))
return -1L;
if (!sel)
@ -948,7 +952,7 @@ static int get_eff_addr_modrm(struct insn *insn, struct pt_regs *regs,
* following instruction.
*/
if (*regoff == -EDOM) {
if (user_64bit_mode(regs))
if (any_64bit_mode(regs))
tmp = regs->ip + insn->length;
else
tmp = 0;
@ -1250,7 +1254,7 @@ static void __user *get_addr_ref_32(struct insn *insn, struct pt_regs *regs)
* After computed, the effective address is treated as an unsigned
* quantity.
*/
if (!user_64bit_mode(regs) && ((unsigned int)eff_addr > seg_limit))
if (!any_64bit_mode(regs) && ((unsigned int)eff_addr > seg_limit))
goto out;
/*