Commit c5cea06b authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon
Browse files

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: default avatarMark Rutland <mark.rutland@arm.com>
Reported-by: default avatarVladimir Murzin <vladimir.murzin@arm.com>
Tested-by: default avatarVladimir Murzin <vladimir.murzin@arm.com>
Fixes: 57f4959b

 ("arm64: kernel: Add support for User Access Override")
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 5edb5649
......@@ -64,8 +64,7 @@ static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
/*
* We need to switch to kernel mode so that we can use __get_user
* to safely read from kernel space. Note that we now dump the
* code first, just in case the backtrace kills us.
* to safely read from kernel space.
*/
fs = get_fs();
set_fs(KERNEL_DS);
......@@ -111,21 +110,12 @@ static void dump_backtrace_entry(unsigned long where)
print_ip_sym(where);
}
static void dump_instr(const char *lvl, struct pt_regs *regs)
static void __dump_instr(const char *lvl, struct pt_regs *regs)
{
unsigned long addr = instruction_pointer(regs);
mm_segment_t fs;
char str[sizeof("00000000 ") * 5 + 2 + 1], *p = str;
int i;
/*
* We need to switch to kernel mode so that we can use __get_user
* to safely read from kernel space. Note that we now dump the
* code first, just in case the backtrace kills us.
*/
fs = get_fs();
set_fs(KERNEL_DS);
for (i = -4; i < 1; i++) {
unsigned int val, bad;
......@@ -139,8 +129,18 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
}
}
printk("%sCode: %s\n", lvl, str);
}
set_fs(fs);
static void dump_instr(const char *lvl, struct pt_regs *regs)
{
if (!user_mode(regs)) {
mm_segment_t fs = get_fs();
set_fs(KERNEL_DS);
__dump_instr(lvl, regs);
set_fs(fs);
} else {
__dump_instr(lvl, regs);
}
}
static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
......
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