1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264
use super::unwindregs::UnwindRegsAarch64;
use crate::add_signed::checked_add_signed;
use crate::error::Error;
use crate::unwind_rule::UnwindRule;
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum UnwindRuleAarch64 {
/// (sp, fp, lr) = (sp, fp, lr)
/// Only possible for the first frame. Subsequent frames must get the
/// return address from somewhere other than the lr register to avoid
/// infinite loops.
NoOp,
/// (sp, fp, lr) = if is_first_frame (sp, fp, lr) else (fp + 16, *fp, *(fp + 8))
/// Used as a fallback rule.
NoOpIfFirstFrameOtherwiseFp,
/// (sp, fp, lr) = (sp + 16x, fp, lr)
/// Only possible for the first frame. Subsequent frames must get the
/// return address from somewhere other than the lr register to avoid
/// infinite loops.
OffsetSp { sp_offset_by_16: u16 },
/// (sp, fp, lr) = (sp + 16x, fp, lr) if is_first_frame
/// This rule reflects an ambiguity in DWARF CFI information. When the
/// return address is "undefined" because it was omitted, it could mean
/// "same value", but this is only allowed for the first frame.
OffsetSpIfFirstFrameOtherwiseStackEndsHere { sp_offset_by_16: u16 },
/// (sp, fp, lr) = (sp + 16x, fp, *(sp + 8y))
OffsetSpAndRestoreLr {
sp_offset_by_16: u16,
lr_storage_offset_from_sp_by_8: i16,
},
/// (sp, fp, lr) = (sp + 16x, *(sp + 8y), *(sp + 8z))
OffsetSpAndRestoreFpAndLr {
sp_offset_by_16: u16,
fp_storage_offset_from_sp_by_8: i16,
lr_storage_offset_from_sp_by_8: i16,
},
/// (sp, fp, lr) = (fp + 16, *fp, *(fp + 8))
UseFramePointer,
/// (sp, fp, lr) = (fp + 8x, *(fp + 8y), *(fp + 8z))
UseFramepointerWithOffsets {
sp_offset_from_fp_by_8: u16,
fp_storage_offset_from_fp_by_8: i16,
lr_storage_offset_from_fp_by_8: i16,
},
}
impl UnwindRule for UnwindRuleAarch64 {
type UnwindRegs = UnwindRegsAarch64;
fn rule_for_stub_functions() -> Self {
UnwindRuleAarch64::NoOp
}
fn rule_for_function_start() -> Self {
UnwindRuleAarch64::NoOp
}
fn fallback_rule() -> Self {
UnwindRuleAarch64::UseFramePointer
}
fn exec<F>(
self,
is_first_frame: bool,
regs: &mut UnwindRegsAarch64,
read_stack: &mut F,
) -> Result<Option<u64>, Error>
where
F: FnMut(u64) -> Result<u64, ()>,
{
let lr = regs.lr();
let sp = regs.sp();
let fp = regs.fp();
let (new_lr, new_sp, new_fp) = match self {
UnwindRuleAarch64::NoOp => {
if !is_first_frame {
return Err(Error::DidNotAdvance);
}
(lr, sp, fp)
}
UnwindRuleAarch64::NoOpIfFirstFrameOtherwiseFp => {
if is_first_frame {
(lr, sp, fp)
} else {
let fp = regs.fp();
let new_sp = fp.checked_add(16).ok_or(Error::IntegerOverflow)?;
let new_lr =
read_stack(fp + 8).map_err(|_| Error::CouldNotReadStack(fp + 8))?;
let new_fp = read_stack(fp).map_err(|_| Error::CouldNotReadStack(fp))?;
if new_sp <= sp {
return Err(Error::FramepointerUnwindingMovedBackwards);
}
(new_lr, new_sp, new_fp)
}
}
UnwindRuleAarch64::OffsetSpIfFirstFrameOtherwiseStackEndsHere { sp_offset_by_16 } => {
if !is_first_frame {
return Ok(None);
}
let sp_offset = u64::from(sp_offset_by_16) * 16;
let new_sp = sp.checked_add(sp_offset).ok_or(Error::IntegerOverflow)?;
(lr, new_sp, fp)
}
UnwindRuleAarch64::OffsetSp { sp_offset_by_16 } => {
if !is_first_frame {
return Err(Error::DidNotAdvance);
}
let sp_offset = u64::from(sp_offset_by_16) * 16;
let new_sp = sp.checked_add(sp_offset).ok_or(Error::IntegerOverflow)?;
(lr, new_sp, fp)
}
UnwindRuleAarch64::OffsetSpAndRestoreLr {
sp_offset_by_16,
lr_storage_offset_from_sp_by_8,
} => {
let sp_offset = u64::from(sp_offset_by_16) * 16;
let new_sp = sp.checked_add(sp_offset).ok_or(Error::IntegerOverflow)?;
let lr_storage_offset = i64::from(lr_storage_offset_from_sp_by_8) * 8;
let lr_location =
checked_add_signed(sp, lr_storage_offset).ok_or(Error::IntegerOverflow)?;
let new_lr =
read_stack(lr_location).map_err(|_| Error::CouldNotReadStack(lr_location))?;
(new_lr, new_sp, fp)
}
UnwindRuleAarch64::OffsetSpAndRestoreFpAndLr {
sp_offset_by_16,
fp_storage_offset_from_sp_by_8,
lr_storage_offset_from_sp_by_8,
} => {
let sp_offset = u64::from(sp_offset_by_16) * 16;
let new_sp = sp.checked_add(sp_offset).ok_or(Error::IntegerOverflow)?;
let lr_storage_offset = i64::from(lr_storage_offset_from_sp_by_8) * 8;
let lr_location =
checked_add_signed(sp, lr_storage_offset).ok_or(Error::IntegerOverflow)?;
let new_lr =
read_stack(lr_location).map_err(|_| Error::CouldNotReadStack(lr_location))?;
let fp_storage_offset = i64::from(fp_storage_offset_from_sp_by_8) * 8;
let fp_location =
checked_add_signed(sp, fp_storage_offset).ok_or(Error::IntegerOverflow)?;
let new_fp =
read_stack(fp_location).map_err(|_| Error::CouldNotReadStack(fp_location))?;
(new_lr, new_sp, new_fp)
}
UnwindRuleAarch64::UseFramePointer => {
// Do a frame pointer stack walk. Frame-based aarch64 functions store the caller's fp and lr
// on the stack and then set fp to the address where the caller's fp is stored.
//
// Function prologue example (this one also stores x19, x20, x21 and x22):
// stp x22, x21, [sp, #-0x30]! ; subtracts 0x30 from sp, and then stores (x22, x21) at sp
// stp x20, x19, [sp, #0x10] ; stores (x20, x19) at sp + 0x10 (== original sp - 0x20)
// stp fp, lr, [sp, #0x20] ; stores (fp, lr) at sp + 0x20 (== original sp - 0x10)
// add fp, sp, #0x20 ; sets fp to the address where the old fp is stored on the stack
//
// Function epilogue:
// ldp fp, lr, [sp, #0x20] ; restores fp and lr from the stack
// ldp x20, x19, [sp, #0x10] ; restores x20 and x19
// ldp x22, x21, [sp], #0x30 ; restores x22 and x21, and then adds 0x30 to sp
// ret ; follows lr to jump back to the caller
//
// Functions are called with bl ("branch with link"); bl puts the return address into the lr register.
// When a function reaches its end, ret reads the return address from lr and jumps to it.
// On aarch64, the stack pointer is always aligned to 16 bytes, and registers are usually written
// to and read from the stack in pairs.
// In frame-based functions, fp and lr are placed next to each other on the stack.
// So when a function is called, we have the following stack layout:
//
// [... rest of the stack]
// ^ sp ^ fp
// bl some_function ; jumps to the function and sets lr = return address
// [... rest of the stack]
// ^ sp ^ fp
// adjust stack ptr, write some registers, and write fp and lr
// [more saved regs] [caller's frame pointer] [return address] [... rest of the stack]
// ^ sp ^ fp
// add fp, sp, #0x20 ; sets fp to where the caller's fp is now stored
// [more saved regs] [caller's frame pointer] [return address] [... rest of the stack]
// ^ sp ^ fp
// <function contents> ; can execute bl and overwrite lr with a new value
// ... [more saved regs] [caller's frame pointer] [return address] [... rest of the stack]
// ^ sp ^ fp
//
// So: *fp is the caller's frame pointer, and *(fp + 8) is the return address.
let fp = regs.fp();
let new_sp = fp.checked_add(16).ok_or(Error::IntegerOverflow)?;
let new_lr = read_stack(fp + 8).map_err(|_| Error::CouldNotReadStack(fp + 8))?;
let new_fp = read_stack(fp).map_err(|_| Error::CouldNotReadStack(fp))?;
if new_fp == 0 {
return Ok(None);
}
if new_fp <= fp || new_sp <= sp {
return Err(Error::FramepointerUnwindingMovedBackwards);
}
(new_lr, new_sp, new_fp)
}
UnwindRuleAarch64::UseFramepointerWithOffsets {
sp_offset_from_fp_by_8,
fp_storage_offset_from_fp_by_8,
lr_storage_offset_from_fp_by_8,
} => {
let sp_offset_from_fp = u64::from(sp_offset_from_fp_by_8) * 8;
let new_sp = fp
.checked_add(sp_offset_from_fp)
.ok_or(Error::IntegerOverflow)?;
let lr_storage_offset = i64::from(lr_storage_offset_from_fp_by_8) * 8;
let lr_location =
checked_add_signed(fp, lr_storage_offset).ok_or(Error::IntegerOverflow)?;
let new_lr =
read_stack(lr_location).map_err(|_| Error::CouldNotReadStack(lr_location))?;
let fp_storage_offset = i64::from(fp_storage_offset_from_fp_by_8) * 8;
let fp_location =
checked_add_signed(fp, fp_storage_offset).ok_or(Error::IntegerOverflow)?;
let new_fp =
read_stack(fp_location).map_err(|_| Error::CouldNotReadStack(fp_location))?;
if new_fp == 0 {
return Ok(None);
}
if new_fp <= fp || new_sp <= sp {
return Err(Error::FramepointerUnwindingMovedBackwards);
}
(new_lr, new_sp, new_fp)
}
};
let return_address = regs.lr_mask().strip_ptr_auth(new_lr);
if return_address == 0 {
return Ok(None);
}
if !is_first_frame && new_sp == sp {
return Err(Error::DidNotAdvance);
}
regs.set_lr(new_lr);
regs.set_sp(new_sp);
regs.set_fp(new_fp);
Ok(Some(return_address))
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_basic() {
let stack = [
1, 2, 3, 4, 0x40, 0x100200, 5, 6, 0x70, 0x100100, 7, 8, 9, 10, 0x0, 0x0,
];
let mut read_stack = |addr| Ok(stack[(addr / 8) as usize]);
let mut regs = UnwindRegsAarch64::new(0x100300, 0x10, 0x20);
let res = UnwindRuleAarch64::NoOp.exec(true, &mut regs, &mut read_stack);
assert_eq!(res, Ok(Some(0x100300)));
assert_eq!(regs.sp(), 0x10);
let res = UnwindRuleAarch64::UseFramePointer.exec(false, &mut regs, &mut read_stack);
assert_eq!(res, Ok(Some(0x100200)));
assert_eq!(regs.sp(), 0x30);
assert_eq!(regs.fp(), 0x40);
let res = UnwindRuleAarch64::UseFramePointer.exec(false, &mut regs, &mut read_stack);
assert_eq!(res, Ok(Some(0x100100)));
assert_eq!(regs.sp(), 0x50);
assert_eq!(regs.fp(), 0x70);
let res = UnwindRuleAarch64::UseFramePointer.exec(false, &mut regs, &mut read_stack);
assert_eq!(res, Ok(None));
}
}