Messages in this thread Patch in this message | | | From | Tony Luck <> | Subject | [PATCH 7/8] x86/mce: Recover from poison found while copying from user space | Date | Tue, 8 Sep 2020 10:55:18 -0700 |
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From: Youquan Song <youquan.song@intel.com>
Existing kernel code can only recover from a machine check on code that tagged in the exception table with a fault handling recovery path.
New field in the task structure mce_vaddr is initialized to the user virtual address of the fault. This is so that kill_me_maybe() can provide that information to the user SIGBUS handler.
Add code to recover from a machine check while copying data from user space to the kernel. Action for this case is the same as if the user touched the poison directly; unmap the page and send a SIGBUS to the task.
Signed-off-by: Youquan Song <youquan.song@intel.com> Signed-off-by: Tony Luck <tony.luck@intel.com> --- arch/x86/kernel/cpu/mce/core.c | 51 ++++++++++++++++++++++++++++++++++ include/linux/sched.h | 1 + 2 files changed, 52 insertions(+)
diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c index 5512318a07ae..2a3c42329c3f 100644 --- a/arch/x86/kernel/cpu/mce/core.c +++ b/arch/x86/kernel/cpu/mce/core.c @@ -53,6 +53,8 @@ #include <asm/mce.h> #include <asm/msr.h> #include <asm/reboot.h> +#include <asm/insn.h> +#include <asm/insn-eval.h> #include "internal.h" @@ -1197,6 +1199,32 @@ static void kill_me_maybe(struct callback_head *cb) kill_me_now(cb); } +/* + * Decode a kernel instruction that faulted while reading from a user + * address and return the linear address that was being read. + */ +static void __user *get_virtual_address(struct pt_regs *regs) +{ + u8 insn_buf[MAX_INSN_SIZE]; + struct insn insn; + + if (copy_from_kernel_nofault(insn_buf, (void *)regs->ip, MAX_INSN_SIZE)) + return (void __user *)~0ul; + + kernel_insn_init(&insn, insn_buf, MAX_INSN_SIZE); + insn_get_length(&insn); + insn_get_modrm(&insn); + insn_get_sib(&insn); + + /* + * For MOVS[BWLQ] the source address is in %rsi + */ + if (insn.opcode.value == 0xa4 || insn.opcode.value == 0xa5) + return (void __user *)regs->si; + else + return insn_get_addr_ref(&insn, regs); +} + /* * The actual machine check handler. This only handles real * exceptions when something got corrupted coming in through int 18. @@ -1342,6 +1370,7 @@ noinstr void do_machine_check(struct pt_regs *regs) /* If this triggers there is no way to recover. Die hard. */ BUG_ON(!on_thread_stack() || !user_mode(regs)); + current->mce_vaddr = NULL; current->mce_addr = m.addr; current->mce_ripv = !!(m.mcgstatus & MCG_STATUS_RIPV); current->mce_whole_page = whole_page(&m); @@ -1350,6 +1379,13 @@ noinstr void do_machine_check(struct pt_regs *regs) current->mce_kill_me.func = kill_me_now; task_work_add(current, ¤t->mce_kill_me, true); } else { + /* + * Before fixing the exception IP, find the user address + * in the MCE_IN_KERNEL_COPYIN case + */ + if (m.kflags & MCE_IN_KERNEL_COPYIN) + current->mce_vaddr = get_virtual_address(regs); + /* * Handle an MCE which has happened in kernel space but from * which the kernel can recover: ex_has_fault_handler() has @@ -1363,6 +1399,21 @@ noinstr void do_machine_check(struct pt_regs *regs) if (!fixup_exception(regs, X86_TRAP_MC, 0, 0)) mce_panic("Failed kernel mode recovery", &m, msg); } + + /* + * MCE on user data while copying to kernel. Action here is + * very similar to the user hitting the poison themself. + * Poison page will be unmapped and signal sent to process. + */ + if (m.kflags & MCE_IN_KERNEL_COPYIN) { + current->mce_addr = m.addr; + current->mce_ripv = !!(m.mcgstatus & MCG_STATUS_RIPV); + current->mce_whole_page = whole_page(&m); + current->mce_kill_me.func = kill_me_maybe; + if (kill_it) + current->mce_kill_me.func = kill_me_now; + task_work_add(current, ¤t->mce_kill_me, true); + } } } EXPORT_SYMBOL_GPL(do_machine_check); diff --git a/include/linux/sched.h b/include/linux/sched.h index afe01e232935..fe384c097ce3 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1308,6 +1308,7 @@ struct task_struct { #endif #ifdef CONFIG_X86_MCE + void __user *mce_vaddr; u64 mce_addr; __u64 mce_ripv : 1, mce_whole_page : 1, -- 2.21.1
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