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| author | Szabolcs Nagy <szabolcs.nagy@arm.com> | 2020-05-13 12:10:13 +0100 |
|---|---|---|
| committer | Szabolcs Nagy <szabolcs.nagy@arm.com> | 2020-06-22 14:53:20 +0100 |
| commit | 8f62ca73284bb85ad0b7a50dfa5a9ecae27bdc0b (patch) | |
| tree | 4254a25a2d3c786e0ed677a74a92ac435b0428ac | |
| parent | abdae6d2900555e7bccbf29d0be6506ea63a43fa (diff) | |
| download | glibc-8f62ca73284bb85ad0b7a50dfa5a9ecae27bdc0b.tar.gz glibc-8f62ca73284bb85ad0b7a50dfa5a9ecae27bdc0b.tar.xz glibc-8f62ca73284bb85ad0b7a50dfa5a9ecae27bdc0b.zip | |
aarch64: fix pac-ret support in _mcount
Currently gcc -pg -mbranch-protection=pac-ret passes signed return address to _mcount, so _mcount now has to always strip pac from the frompc since that's from user code that may be built with pac-ret. This is gcc PR target/94791: signed pointers should not escape and get passed across extern call boundaries, since that's an ABI break, but because existing gcc has this issue we work it around in glibc until that is resolved. This is compatible with a fixed gcc and it is a nop on systems without PAuth support. The bug was introduced in gcc-7 with -msign-return-address=non-leaf|all support which in gcc-9 got renamed to -mbranch-protection=pac-ret|pac-ret+leaf|standard. strip_pac uses inline asm instead of __builtin_aarch64_xpaclri since that is not a documented api and not available in all supported gccs.
| -rw-r--r-- | sysdeps/aarch64/machine-gmon.h | 3 | ||||
| -rw-r--r-- | sysdeps/aarch64/sysdep.h | 11 |
2 files changed, 13 insertions, 1 deletions
diff --git a/sysdeps/aarch64/machine-gmon.h b/sysdeps/aarch64/machine-gmon.h index 730a23b781..a687298b1c 100644 --- a/sysdeps/aarch64/machine-gmon.h +++ b/sysdeps/aarch64/machine-gmon.h @@ -27,8 +27,9 @@ static void mcount_internal (u_long frompc, u_long selfpc); #define _MCOUNT_DECL(frompc, selfpc) \ static inline void mcount_internal (u_long frompc, u_long selfpc) +/* Note: strip_pac is needed for frompc because of gcc PR target/94791. */ #define MCOUNT \ void __mcount (void *frompc) \ { \ - mcount_internal ((u_long) frompc, (u_long) RETURN_ADDRESS (0)); \ + mcount_internal ((u_long) strip_pac (frompc), (u_long) RETURN_ADDRESS (0)); \ } diff --git a/sysdeps/aarch64/sysdep.h b/sysdeps/aarch64/sysdep.h index 500c272745..2879aeaa5c 100644 --- a/sysdeps/aarch64/sysdep.h +++ b/sysdeps/aarch64/sysdep.h @@ -35,6 +35,17 @@ #define PTR_SIZE (1<<PTR_LOG_SIZE) +#ifndef __ASSEMBLER__ +/* Strip pointer authentication code from pointer p. */ +static inline void * +strip_pac (void *p) +{ + register void *ra asm ("x30") = (p); + asm ("hint 7 // xpaclri" : "+r"(ra)); + return ra; +} +#endif + #ifdef __ASSEMBLER__ /* Syntactic details of assembler. */ |