On Mon, Jun 17, 2019 at 05:23:04PM +0200, Mathieu Desnoyers wrote: > This reverts commit 2b845d4b4acd9422bbb668989db8dc36dfc8f438. > > That commit introduces build issues for programs compiled in Thumb mode. > Rather than try to be clever and emit a valid trap instruction on arm32, > which requires special care about big/little endian handling on that > architecture, just emit plain data. Data in the instruction stream is > technically expected on arm32: this is how literal pools are > implemented. Reverting to the prior behavior does exactly that. > > Signed-off-by: Mathieu Desnoyers <[email protected]> > CC: Peter Zijlstra <[email protected]> > CC: Thomas Gleixner <[email protected]> > CC: Joel Fernandes <[email protected]> > CC: Catalin Marinas <[email protected]> > CC: Dave Watson <[email protected]> > CC: Will Deacon <[email protected]> > CC: Shuah Khan <[email protected]> > CC: Andi Kleen <[email protected]> > CC: [email protected] > CC: "H . Peter Anvin" <[email protected]> > CC: Chris Lameter <[email protected]> > CC: Russell King <[email protected]> > CC: Michael Kerrisk <[email protected]> > CC: "Paul E . McKenney" <[email protected]> > CC: Paul Turner <[email protected]> > CC: Boqun Feng <[email protected]> > CC: Josh Triplett <[email protected]> > CC: Steven Rostedt <[email protected]> > CC: Ben Maurer <[email protected]> > CC: [email protected] > CC: Andy Lutomirski <[email protected]> > CC: Andrew Morton <[email protected]> > CC: Linus Torvalds <[email protected]> > CC: Carlos O'Donell <[email protected]> > CC: Florian Weimer <[email protected]> > --- > tools/testing/selftests/rseq/rseq-arm.h | 52 > ++------------------------------- > 1 file changed, 2 insertions(+), 50 deletions(-) > > diff --git a/tools/testing/selftests/rseq/rseq-arm.h > b/tools/testing/selftests/rseq/rseq-arm.h > index 84f28f147fb6..5f262c54364f 100644 > --- a/tools/testing/selftests/rseq/rseq-arm.h > +++ b/tools/testing/selftests/rseq/rseq-arm.h > @@ -5,54 +5,7 @@ > * (C) Copyright 2016-2018 - Mathieu Desnoyers > <[email protected]> > */ > > -/* > - * RSEQ_SIG uses the udf A32 instruction with an uncommon immediate operand > - * value 0x5de3. This traps if user-space reaches this instruction by > mistake, > - * and the uncommon operand ensures the kernel does not move the instruction > - * pointer to attacker-controlled code on rseq abort. > - * > - * The instruction pattern in the A32 instruction set is: > - * > - * e7f5def3 udf #24035 ; 0x5de3 > - * > - * This translates to the following instruction pattern in the T16 > instruction > - * set: > - * > - * little endian: > - * def3 udf #243 ; 0xf3 > - * e7f5 b.n <7f5> > - * > - * pre-ARMv6 big endian code: > - * e7f5 b.n <7f5> > - * def3 udf #243 ; 0xf3 > - * > - * ARMv6+ -mbig-endian generates mixed endianness code vs data: little-endian > - * code and big-endian data. Ensure the RSEQ_SIG data signature matches code > - * endianness. Prior to ARMv6, -mbig-endian generates big-endian code and > data > - * (which match), so there is no need to reverse the endianness of the data > - * representation of the signature. However, the choice between BE32 and BE8 > - * is done by the linker, so we cannot know whether code and data endianness > - * will be mixed before the linker is invoked. > - */ > - > -#define RSEQ_SIG_CODE 0xe7f5def3 > - > -#ifndef __ASSEMBLER__ > - > -#define RSEQ_SIG_DATA > \ > - ({ \ > - int sig; \ > - asm volatile ("b 2f\n\t" \ > - "1: .inst " __rseq_str(RSEQ_SIG_CODE) "\n\t" \ > - "2:\n\t" \ > - "ldr %[sig], 1b\n\t" \ > - : [sig] "=r" (sig)); \ > - sig; \ > - }) > - > -#define RSEQ_SIG RSEQ_SIG_DATA > - > -#endif > +#define RSEQ_SIG 0x53053053
I don't get why you're reverting back to this old signature value, when the one we came up with will work well when interpreted as an instruction in the *vast* majority of scenarios that people care about (A32/T32 little-endian). I think you might be under-estimating just how dead things like BE32 really are. That said, when you ran into .inst.n/.inst.w issues, did you try something along the lines of the WASM() macro we use in arch/arm/, which adds the ".w" suffix when targetting Thumb? Will
