From 3d31bc39e655ea39721754fa0ea539a8a0c9b26c Mon Sep 17 00:00:00 2001 From: Alan Hayward Date: Wed, 7 Aug 2019 09:47:57 +0100 Subject: AArch64 pauth: Indicate unmasked addresses in backtrace Armv8.3-a Pointer Authentication causes the function return address to be obfuscated on entry to some functions. GDB must unmask the link register in order to produce a backtrace. The following patch adds markers of [PAC] to the bracktrace, to indicate which addresses needed unmasking. This includes the backtrace when using MI. For example, consider the following backtrace: (gdb) bt 0 0x0000000000400490 in puts@plt () 1 0x00000000004005dc in foo ("hello") at cbreak-lib.c:6 2 0x0000000000400604 [PAC] in bar () at cbreak-lib.c:12 3 0x0000000000400620 [PAC] in main2 () at cbreak.c:17 4 0x00000000004005b4 in main () at cbreak-3.c:10 The functions in cbreak-lib use pointer auth, which masks the return address to the previous function, causing the addresses of bar (in the library) and main2 (in the main binary) to require unmasking in order to unwind the backtrace. An extra bool is added alongside the prev_pc in the frame structure. At the point at which the link register is unmasked, the AArch64 port calls into frame to sets the bool. This is the most efficient way of doing it. The marker is also added to the python frame printer, which is always printed if set. The marker is not explicitly exposed to the python code. I expect this will potentially cause issues with some tests in the testsuite when Armv8.3 pointer authentication is used. This should be fixed up in the the future once real hardware is available for full testsuite testing. gdb/ChangeLog: * NEWS: Expand the Pointer Authentication entry. * aarch64-tdep.c (aarch64_frame_unmask_address): Rename from this. (aarch64_frame_unmask_lr): ... to this. (aarch64_prologue_prev_register, aarch64_dwarf2_prev_register): Call aarch64_frame_unmask_lr. * frame.c (struct frame_info): Add "masked" variable. (frame_set_previous_pc_masked) (frame_get_pc_masked): New functions. (fprint_frame): Check for masked pc. * frame.h (frame_set_previous_pc_masked) (frame_get_pc_masked): New declarations. * python/py-framefilter.c (py_print_frame): Check for masked pc. * stack.c (print_frame): Check for masked pc. gdb/doc/ChangeLog: * gdb.texinfo (AArch64 Pointer Authentication): New subsection. --- gdb/frame.h | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'gdb/frame.h') diff --git a/gdb/frame.h b/gdb/frame.h index ccc2850..fdb401d 100644 --- a/gdb/frame.h +++ b/gdb/frame.h @@ -949,4 +949,13 @@ extern const gdb::option::option_def set_backtrace_option_defs[2]; /* The values behind the global "set backtrace ..." settings. */ extern set_backtrace_options user_set_backtrace_options; +/* Mark that the PC value is masked for the previous frame. */ + +extern void set_frame_previous_pc_masked (struct frame_info *frame); + +/* Get whether the PC value is masked for the given frame. */ + +extern bool get_frame_pc_masked (const struct frame_info *frame); + + #endif /* !defined (FRAME_H) */ -- cgit v1.1