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arm64/module: switch to ADRP/ADD sequences for PLT entries

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Now that we have switched to the small code model entirely, and
reduced the extended KASLR range to 4 GB, we can be sure that the
targets of relative branches that are out of range are in range
for a ADRP/ADD pair, which is one instruction shorter than our
current MOVN/MOVK/MOVK sequence, and is more idiomatic and so it
is more likely to be implemented efficiently by micro-architectures.

So switch over the ordinary PLT code and the special handling of
the Cortex-A53 ADRP errata, as well as the ftrace trampline
handling.

Reviewed-by: Torsten Duwe <duwe@lst.de>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
[will: Added a couple of comments in the plt equality check]
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Ard Biesheuvel
2018-11-22 09:46:46 +01:00
committed by Will Deacon
parent 7aaf7b2fd2
commit bdb85cd1d2
4 changed files with 88 additions and 53 deletions
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36
arch/arm64/include/asm/module.h
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@@ -58,39 +58,19 @@ struct plt_entry {
* is exactly what we are dealing with here, we are free to use x16
* as a scratch register in the PLT veneers.
*/
__le32 mov0; /* movn x16, #0x.... */
__le32 mov1; /* movk x16, #0x...., lsl #16 */
__le32 mov2; /* movk x16, #0x...., lsl #32 */
__le32 adrp; /* adrp x16, .... */
__le32 add; /* add x16, x16, #0x.... */
__le32 br; /* br x16 */
};
static inline struct plt_entry get_plt_entry(u64 val)
static inline bool is_forbidden_offset_for_adrp(void *place)
{
/*
* MOVK/MOVN/MOVZ opcode:
* +--------+------------+--------+-----------+-------------+---------+
* | sf[31] | opc[30:29] | 100101 | hw[22:21] | imm16[20:5] | Rd[4:0] |
* +--------+------------+--------+-----------+-------------+---------+
*
* Rd := 0x10 (x16)
* hw := 0b00 (no shift), 0b01 (lsl #16), 0b10 (lsl #32)
* opc := 0b11 (MOVK), 0b00 (MOVN), 0b10 (MOVZ)
* sf := 1 (64-bit variant)
*/
return (struct plt_entry){
cpu_to_le32(0x92800010 | (((~val ) & 0xffff)) << 5),
cpu_to_le32(0xf2a00010 | ((( val >> 16) & 0xffff)) << 5),
cpu_to_le32(0xf2c00010 | ((( val >> 32) & 0xffff)) << 5),
cpu_to_le32(0xd61f0200)
};
return IS_ENABLED(CONFIG_ARM64_ERRATUM_843419) &&
cpus_have_const_cap(ARM64_WORKAROUND_843419) &&
((u64)place & 0xfff) >= 0xff8;
}
static inline bool plt_entries_equal(const struct plt_entry *a,
const struct plt_entry *b)
{
return a->mov0 == b->mov0 &&
a->mov1 == b->mov1 &&
a->mov2 == b->mov2;
}
struct plt_entry get_plt_entry(u64 dst, void *pc);
bool plt_entries_equal(const struct plt_entry *a, const struct plt_entry *b);
#endif /* __ASM_MODULE_H */