On 5/26/21 8:25 AM, Babu Moger wrote: > On 5/25/21 7:20 PM, Dave Hansen wrote: >> On 5/25/21 5:03 PM, Babu Moger wrote: >>>> What values do PKRU and the shadow have when the test fails? Is PKRU 0? >>> It goes back to default value 0x55555554. The test is expecting it to be >>> 0. Printed them below. >>> >>> test_ptrace_of_child()::1346, pkey_reg: 0x0000000055555554 shadow: >>> 0000000000000000 >>> protection_keys_64: pkey-helpers.h:127: _read_pkey_reg: Assertion >>> `pkey_reg == shadow_pkey_reg' failed. >> That's backwards (shadow vs pkru) from what I was expecting. >> >> Can you turn on all the debuging? >> >> Just compile with -DDEBUG_LEVEL=5 > > Copied the logs at https://pastebin.com/gtQiHg8Q Well, it's a bit backwards from what I'm expecting. The PKRU=0 value *WAS* legitimate because all of the pkeys got allocated and their disable bits cleared. I think Andy was close when he was blaming: > static inline void write_pkru(u32 pkru) > { ... > pk = get_xsave_addr(¤t->thread.fpu.state.xsave, XFEATURE_PKRU); ... > if (pk) > pk->pkru = pkru; > __write_pkru(pkru); > } But that can't be it because PKRU ended up with 0x55555554. Something must have been writing 'init_pkru_value'. switch_fpu_finish() does that: > static inline void switch_fpu_finish(struct fpu *new_fpu) > { > u32 pkru_val = init_pkru_value; ... > if (current->mm) { > pk = get_xsave_addr(&new_fpu->state.xsave, XFEATURE_PKRU); > if (pk) > pkru_val = pk->pkru; > } > __write_pkru(pkru_val); ... > } If 'new_fpu' had XSTATE_BV[PKRU]=0 then we'd have pk=NULL and 'pkru_val' would still have 'init_pkru_value'. *Then*, we'd have a shadow=0x0 and pkru=0x55555554. It would also only trigger if the hardware has an init tracker that fires when wrpkru(0). Intel doesn't do that. AMD must. Anyway, I need to think about this a bit more. But, an entirely guaranteed to be 100% untested patch is attached. I'm *NOT* confident this is the right fix. I don't have much AMD hardware laying around, so testing would be appreciated.
diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h index 8d33ad8..21402eb 100644 --- a/arch/x86/include/asm/fpu/internal.h +++ b/arch/x86/include/asm/fpu/internal.h @@ -582,6 +582,8 @@ static inline void switch_fpu_finish(struct fpu *new_fpu) pk = get_xsave_addr(&new_fpu->state.xsave, XFEATURE_PKRU); if (pk) pkru_val = pk->pkru; + else + pkru_val = 0x0; } __write_pkru(pkru_val);
