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Date: Fri, 03 Apr 2015 13:52:00 +0200 From: Denys Vlasenko <dvlasenk@...hat.com> To: Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org> CC: LKML <linux-kernel@...r.kernel.org>, Andy Lutomirski <luto@...capital.net>, Alexei Starovoitov <ast@...mgrid.com>, Frederic Weisbecker <fweisbec@...il.com>, "H. Peter Anvin" <hpa@...or.com>, Kees Cook <keescook@...omium.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Oleg Nesterov <oleg@...hat.com>, Steven Rostedt <rostedt@...dmis.org>, Will Drewry <wad@...omium.org> Subject: Re: [PATCH] x86/asm/entry/64: Fix MSR_IA32_SYSENTER_CS MSR value On 04/03/2015 01:20 PM, Borislav Petkov wrote: > On Fri, Apr 03, 2015 at 11:42:10AM +0200, Borislav Petkov wrote: >> From: Borislav Petkov <bp@...e.de> >> >> Commit >> >> d56fe4bf5f3c ("x86/asm/entry/64: Always set up SYSENTER MSRs") >> >> missed to add "ULL" to the 0 and wrmsrl_safe() complains: >> >> arch/x86/kernel/cpu/common.c: In function ‘syscall_init’: >> arch/x86/kernel/cpu/common.c:1226:2: warning: right shift count >= width of type >> wrmsrl_safe(MSR_IA32_SYSENTER_CS, 0); >> >> Fix it. >> >> Signed-off-by: Borislav Petkov <bp@...e.de> >> Cc: Denys Vlasenko <dvlasenk@...hat.com> >> Cc: Andy Lutomirski <luto@...capital.net> >> Cc: Alexei Starovoitov <ast@...mgrid.com> >> Cc: Frederic Weisbecker <fweisbec@...il.com> >> Cc: H. Peter Anvin <hpa@...or.com> >> Cc: Kees Cook <keescook@...omium.org> >> Cc: Linus Torvalds <torvalds@...ux-foundation.org> >> Cc: Oleg Nesterov <oleg@...hat.com> >> Cc: Steven Rostedt <rostedt@...dmis.org> >> Cc: Will Drewry <wad@...omium.org> >> Cc: Ingo Molnar <mingo@...nel.org> >> --- >> arch/x86/kernel/cpu/common.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c >> index bb6633a87a19..2c249b57e4b5 100644 >> --- a/arch/x86/kernel/cpu/common.c >> +++ b/arch/x86/kernel/cpu/common.c >> @@ -1223,7 +1223,7 @@ void syscall_init(void) >> wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)ia32_sysenter_target); >> #else >> wrmsrl(MSR_CSTAR, ignore_sysret); >> - wrmsrl_safe(MSR_IA32_SYSENTER_CS, 0); >> + wrmsrl_safe(MSR_IA32_SYSENTER_CS, 0ULL); > > Btw, we probably should define an invalid segment > > #define GDT_ENTRY_INVALID_SEGMENT 0ULL > > and use that value instead of the naked 0. Why? Segment selectors aren't "long long", they are in fact "short" (16-bit ints). The "ULL" is used here in wrmsrl not because it's a segment, but because wrmsrl expects a u64 parameter. We can probably add a cast in its definition... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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