arm64: fix dump_instr when PAN and UAO are in use
If the kernel is set to show unhandled signals, and a user task does not handle a SIGILL as a result of an instruction abort, we will attempt to log the offending instruction with dump_instr before killing the task. We use dump_instr to log the encoding of the offending userspace instruction. However, dump_instr is also used to dump instructions from kernel space, and internally always switches to KERNEL_DS before dumping the instruction with get_user. When both PAN and UAO are in use, reading a user instruction via get_user while in KERNEL_DS will result in a permission fault, which leads to an Oops. As we have regs corresponding to the context of the original instruction abort, we can inspect this and only flip to KERNEL_DS if the original abort was taken from the kernel, avoiding this issue. At the same time, remove the redundant (and incorrect) comments regarding the order dump_mem and dump_instr are called in. Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: James Morse <james.morse@arm.com> Cc: Robin Murphy <robin.murphy@arm.com> Cc: <stable@vger.kernel.org> #4.6+ Signed-off-by: Mark Rutland <mark.rutland@arm.com> Reported-by: Vladimir Murzin <vladimir.murzin@arm.com> Tested-by: Vladimir Murzin <vladimir.murzin@arm.com> Fixes: 57f4959bad0a154a ("arm64: kernel: Add support for User Access Override") Signed-off-by: Will Deacon <will.deacon@arm.com>
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@ -64,8 +64,7 @@ static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
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/*
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* We need to switch to kernel mode so that we can use __get_user
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* to safely read from kernel space. Note that we now dump the
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* code first, just in case the backtrace kills us.
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* to safely read from kernel space.
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*/
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fs = get_fs();
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set_fs(KERNEL_DS);
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@ -111,21 +110,12 @@ static void dump_backtrace_entry(unsigned long where)
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print_ip_sym(where);
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}
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static void dump_instr(const char *lvl, struct pt_regs *regs)
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static void __dump_instr(const char *lvl, struct pt_regs *regs)
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{
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unsigned long addr = instruction_pointer(regs);
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mm_segment_t fs;
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char str[sizeof("00000000 ") * 5 + 2 + 1], *p = str;
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int i;
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/*
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* We need to switch to kernel mode so that we can use __get_user
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* to safely read from kernel space. Note that we now dump the
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* code first, just in case the backtrace kills us.
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*/
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fs = get_fs();
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set_fs(KERNEL_DS);
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for (i = -4; i < 1; i++) {
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unsigned int val, bad;
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@ -139,8 +129,18 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
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}
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}
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printk("%sCode: %s\n", lvl, str);
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}
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set_fs(fs);
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static void dump_instr(const char *lvl, struct pt_regs *regs)
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{
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if (!user_mode(regs)) {
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mm_segment_t fs = get_fs();
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set_fs(KERNEL_DS);
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__dump_instr(lvl, regs);
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set_fs(fs);
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} else {
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__dump_instr(lvl, regs);
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}
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}
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static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
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