From 7be4412721aee25e35583a20a896085dc6b99c3e Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Thu, 19 Dec 2019 00:11:47 +0100 Subject: [PATCH] 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 Signed-off-by: Borislav Petkov Cc: Alexander Potapenko Cc: Andrey Konovalov Cc: Andrey Ryabinin Cc: Andy Lutomirski Cc: Dmitry Vyukov Cc: "Gustavo A. R. Silva" Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: kasan-dev@googlegroups.com Cc: Oleg Nesterov Cc: Sean Christopherson Cc: Thomas Gleixner Cc: x86-ml Link: https://lkml.kernel.org/r/20191218231150.12139-1-jannh@google.com --- arch/x86/include/asm/ptrace.h | 13 +++++++++++++ arch/x86/lib/insn-eval.c | 26 +++++++++++++++----------- 2 files changed, 28 insertions(+), 11 deletions(-) diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h index 5057a8ed100b..ac45b06941a5 100644 --- a/arch/x86/include/asm/ptrace.h +++ b/arch/x86/include/asm/ptrace.h @@ -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 diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 306c3a0902ba..31600d851fd8 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -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; /*