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Wed, 2 Jul 2025 01:35:44 +0000 Message-ID: <95dc18fd-73b0-4019-92d2-c0e6aaf22c96@intel.com> Date: Tue, 1 Jul 2025 18:35:40 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv8 14/17] x86/traps: Handle LASS thrown #SS Content-Language: en-US To: "Kirill A. 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Shutemov wrote: > LASS throws a #GP for any violations except for stack register accesses, > in which case it throws a #SS instead. Handle this similarly to how other > LASS violations are handled. > Maybe I've misunderstood something: Is the underlying assumption here that #SS were previously only generated by userspace, but now they can also be generated by the kernel? And we want the kernel generated #SS to behave the same as the #GP? > In case of FRED, before handling #SS as LASS violation, kernel has to > check if there's a fixup for the exception. It can address #SS due to > invalid user context on ERETU. See 5105e7687ad3 ("x86/fred: Fixup > fault on ERETU by jumping to fred_entrypoint_user") for more details. > > Co-developed-by: Alexander Shishkin > Signed-off-by: Alexander Shishkin > Signed-off-by: Kirill A. Shutemov > --- > arch/x86/kernel/traps.c | 39 +++++++++++++++++++++++++++++++++------ > 1 file changed, 33 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > index ceb091f17a5b..f9ca5b911141 100644 > --- a/arch/x86/kernel/traps.c > +++ b/arch/x86/kernel/traps.c > @@ -418,12 +418,6 @@ DEFINE_IDTENTRY_ERRORCODE(exc_segment_not_present) > SIGBUS, 0, NULL); > } > > -DEFINE_IDTENTRY_ERRORCODE(exc_stack_segment) > -{ > - do_error_trap(regs, error_code, "stack segment", X86_TRAP_SS, SIGBUS, > - 0, NULL); > -} > - > DEFINE_IDTENTRY_ERRORCODE(exc_alignment_check) > { > char *str = "alignment check"; > @@ -866,6 +860,39 @@ DEFINE_IDTENTRY_ERRORCODE(exc_general_protection) > cond_local_irq_disable(regs); > } > > +#define SSFSTR "stack segment fault" > + > +DEFINE_IDTENTRY_ERRORCODE(exc_stack_segment) > +{ > + if (user_mode(regs)) > + goto error_trap; > + > + if (cpu_feature_enabled(X86_FEATURE_FRED) && > + fixup_exception(regs, X86_TRAP_SS, error_code, 0)) > + return; > + > + if (cpu_feature_enabled(X86_FEATURE_LASS)) { > + enum kernel_exc_hint hint; > + unsigned long exc_addr; > + > + hint = get_kernel_exc_address(regs, &exc_addr); > + if (hint != EXC_NO_HINT) { The brackets are not needed for singular statements. Also the max line length is longer now. You can fit this all in a single line. > + printk(SSFSTR ", %s 0x%lx", kernel_exc_hint_help[hint], > + exc_addr); > + } > + > + if (hint != EXC_NON_CANONICAL) > + exc_addr = 0; > + > + die_addr(SSFSTR, regs, error_code, exc_addr); The variable names in die_addr() should be generalized as well. They seem to assume the caller to be a #GP handler. > + return; > + } > + > +error_trap: > + do_error_trap(regs, error_code, "stack segment", X86_TRAP_SS, SIGBUS, > + 0, NULL); > +} > + > static bool do_int3(struct pt_regs *regs) > { > int res;