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Tue, 09 Apr 2024 05:50:57 -0700 (PDT) From: Roger Pau Monne To: xen-devel@lists.xenproject.org Cc: Roger Pau Monne , Jan Beulich , Andrew Cooper Subject: [PATCH] x86/alternatives: fix .init section reference in _apply_alternatives() Date: Tue, 9 Apr 2024 14:50:46 +0200 Message-ID: <20240409125046.60382-1-roger.pau@citrix.com> X-Mailer: git-send-email 2.44.0 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-ZohoMail-DKIM: pass (identity @citrix.com) X-ZM-MESSAGEID: 1712667085933100001 The code in _apply_alternatives() will unconditionally attempt to read __initdata_cf_clobber_{start,end} when called as part of applying alternati= ves to a livepatch payload. That leads to a page-fault as __initdata_cf_clobber_{start,end} living in .init section will have been unmapped by the time a livepatch gets loaded. Fix by adding a check that limits the clobbering of endbr64 instructions to boot time only. Fixes: 37ed5da851b8 ('x86/altcall: Optimise away endbr64 instruction where = possible') Signed-off-by: Roger Pau Monn=C3=A9 Reviewed-by: Andrew Cooper --- xen/arch/x86/alternative.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/xen/arch/x86/alternative.c b/xen/arch/x86/alternative.c index 21af0e825822..2e7ba6e0b833 100644 --- a/xen/arch/x86/alternative.c +++ b/xen/arch/x86/alternative.c @@ -326,7 +326,7 @@ static void init_or_livepatch _apply_alternatives(struc= t alt_instr *start, * Clobber endbr64 instructions now that altcall has finished optimisi= ng * all indirect branches to direct ones. */ - if ( force && cpu_has_xen_ibt ) + if ( force && cpu_has_xen_ibt && system_state < SYS_STATE_active ) { void *const *val; unsigned int clobbered =3D 0; --=20 2.44.0